Rapid thermal processing apparatus for processing semiconductor wafers

ABSTRACT

A novel rapid thermal process (RTP) reactor processes a multiplicity of wafers or a single large wafer, e.g., 200 mm (8 inches), 250 mm (10 inches), 300 mm (12 inches) diameter wafers, using either a single or dual heat source. The wafers or wafer are mounted on a rotatable susceptor supported by a susceptor support. A susceptor position control rotates the wafers during processing and raises and lowers the susceptor to various positions for loading and processing of wafers. A heat controller controls either a single heat source or a dual heat source that heats the wafers to a substantially uniform temperature during processing. A gas flow controller regulates flow of gases into the reaction chamber. Instead of the second heat source, a passive heat distribution is used, in one embodiment, to achieve a substantially uniform temperature throughout the wafers. Further, a novel susceptor is used that includes a silicon carbide cloth enclosed in quartz.

This application is a continuation of application Ser. No. 08/007,981,filed Jan. 21, 1993, now U.S. Pat. No. 5,444,217.

CROSS-REFERENCE TO MICROFICHE APPENDIX

Appendix A, which is a part of the present disclosure, is a microficheappendix consisting of 3 sheets of microfiche having a total of 228frames. Microfiche Appendix A is a listing of computer programs andrelated data in one embodiment of this invention, which is describedmore completely below.

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent files or records, but otherwise reserves all copyrightrights whatsoever.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to processing semiconductor wafers,and, in particular, to a method and apparatus for rapid thermalprocessing of a plurality of semiconductor wafers simultaneously and ofa single large semiconductor wafer.

2. Related Art

Deposition of a film on the surface of a semiconductor wafer is a commonstep in semiconductor processing. Typically, selected chemical gases aremixed in a deposition chamber containing a semiconductor wafer. Usually,heat is applied to drive the chemical reaction of the gases in thechamber and to heat the surface of the wafer on which the film isdeposited.

In deposition processes, it is desirable to maximize wafer throughput(i.e., the number of wafers processed per unit time), while depositingfilm layers that have uniform thickness and resistivity. To obtainuniform thickness and resistivity, it is important to maintain the waferat a uniform temperature.

A number of different deposition reactors have been developed.Generally, each deposition reactor has a reaction chamber, a waferhandling system, a heat source and temperature control, and a gasdelivery system (inlet, exhaust, flow control).

FIG. 1A is a simplified cross-sectional view of one type of prior artdeposition reactor 100, known as a horizontal furnace, in whichsusceptor 101 is positioned in horizontal tube 102 (usually ofrectangular cross-section), the interior of which is the reactionchamber. Semiconductor wafers, 103a, 103b, and 103c are mounted onsurface 101a of susceptor 101. Heat source 104 heats the wafers, andreactant gases 105 are flowed through tube 102 past the wafers.Susceptor 101 is often tilted, as shown in FIG. 1A, so that surface 101afaces into the flow of reactant gases 105 to minimize the problem ofreactant depletion in the vicinity of the wafers near the end of theflow of reactant gases 105.

FIG. 1B is a simplified orthogonal view of another type of prior artreactor 110, known as a barrel reactor, in which susceptor 111 issuspended in the interior of bell jar 112 which defines the reactionchamber. Semiconductor wafers, e.g., wafer 113, are mountedsubstantially vertically on the sides, e.g., side 111a, of susceptor111. Heat source 114 heats the wafers, and reactant gases are introducedthrough gas inlet 115 into the top of bell jar 112. The gases pass downthe length of susceptor 111, over the surfaces of the wafers, and areexhausted from the reaction chamber through a gas outlet (not shown) atthe bottom of bell jar 112.

FIG. 1C is a simplified cross-sectional view of yet another type ofprior art conventional chemical vapor deposition reactor 120, known as apancake reactor, in which vertically fixed susceptor 121 is supportedfrom the bottom of bell jar 122 which defines the reaction chamber.Semiconductor wafers, e.g., wafer 123, are mounted horizontally onsurface 121a of susceptor 121. The wafers are heated by a RF heat source(not shown), and reactant gases are introduced into the reaction chamberabove the wafers through susceptor support 125. The gases flow down overthe wafers and are exhausted through a gas outlet (not shown) at thebottom of bell jar 122.

Deposition reactors may be classified according to characteristics oftheir operation. For instance, a reactor may be either cold wall or hotwall. Cold wall reactors are usually preferred because undesirabledeposits do not build up on the chamber walls.

A reactor may also be characterized by the amount of time that isrequired to heat up and cool down the wafer. Conventional reactors takeon the order of 40-90 minutes for a complete process cycle of a batch ofwafers. Rapid thermal process (RTP) reactors, on the other hand, requireonly 2-15 minutes to process a wafer. Thus, rapid thermal reactors arecharacterized by the fact that the process cycle time is significantlyless than the process cycle time for a conventional reactor.

Conventional reactors have been used to process a plurality of wafers ora single wafer in one batch, while RTP reactors have been used toprocess single wafer batches. RTP reactors have not been used forprocessing multiple wafer batches because the rapid temperature changesin RTP reactors make it difficult to achieve a uniform temperature areain the reaction chamber. The area of the reaction chamber with a uniformtemperature limits the operation to a single wafer, typically with adiameter of 200 mm (8 inches) or less.

While RTP reactors have been used to process one wafer at a time, asopposed to the multiple wafer processing of conventional reactors, theone wafer batch capacity of the RTP reactor has been acceptable onlybecause these reactors achieve more uniform resistivities andthicknesses than possible with conventional reactors. In conventionalreactors, thickness and resistivity variations of 3-10% are achievable.In RTP reactors, thickness variations of 1-2% and resistivity variationsof 1-5% are achievable.

A reactor may also be characterized according to the orientation of thewafer in the reaction chamber. A vertical reactor is one in which thesurface on which gases are deposited is substantially vertical. Ahorizontal reactor is one in which the surface on which gases aredeposited is substantially horizontal.

A reactor may also be characterized according to the type of heat sourceused to heat the wafers. Use of radiant heating for semiconductorprocessing is known in the prior art and relates back to the latesixties. A variety of systems have been developed for semiconductorprocessing which include either a radiant energy heat source, or a RFenergy heat source, and a susceptor. However, each of these apparatus'suffer from one or more problems.

Sheets, U.S. Pat. No. 4,649,261 entitled "Apparatus for HeatingSemiconductor Wafers in Order To Achieve Annealing, Silicide Formation,Reflow of Glass, Passivation Layers, etc.", used two radiant heatsources--a continuous wave and a pulsed heat source--to heat astationary wafer at 200° C. to 500° C. per second. Shimizu, U.S. Pat.No. 4,533,820 entitled "Radiant Heating Apparatus", shows a reactionchamber surrounded by a plurality of planar light sources which heat asemiconductor wafer supported by a pedestal. Shimizu reported that auniform oxide film was formed on the semiconductor wafer within threeminutes after the lights were turned-on.

Other configurations using dual radiant heat sources to heat asemiconductor wafer are shown, for example, in U.S. Pat. No. 4,680,451,entitled "Apparatus Using High Intensity CW Lamps for Improved HeatTreating of Semiconductor Wafer," issued to Gat et al. on Jul. 14, 1987and U.S. Pat. No. 4,550,245, entitled "Light-Radiant Furnace for HeatingSemiconductor Wafers," issued to Arai et al., on Oct. 29, 1985. Gat etal reported heating a four inch wafer to 700° C. in three seconds,maintaining the temperature for ten seconds, and then ramping thetemperature down in three seconds. Arai et al. reported applying 1600watts to each of the lamps in the radiant heat source to heat a siliconwafer of 450 μm in thickness and 4 inches square in area to atemperature of 1200° C. within 10 seconds of when power was applied tothe lamps.

In yet another apparatus for heating a semiconductor wafer, Robinson etal., U.S. Pat. No. 4,789,771, a wafer is supported above a susceptor ina reaction chamber. Infrared heat lamps extend directly through thereaction chamber. This design suffers from several shortcomings. Theradiant heat lamps are exposed to the gases in the reaction chamberallowing deposits to form on the lamps. Additionally, the only coolingmechanism for the lamps and the inner surface of the reflectors is thegas flow through the chamber; consequently, lamp lifetime is probablyadversely affected. Further, the reflectors are apparently at anelevated temperature, as well as the quartz sheets around the radiantenergy bulbs so that, over time, deposits are formed on the bulb andreflector surfaces which, in turn, will affect the uniformity of layersformed on the susceptor. Last, special mechanisms are required touniformly heat the susceptor surface because the susceptor rotationmechanism, which is typically opaque to radiant energy, prevents directheating of the entire lower surface of the susceptor.

SUMMARY OF THE INVENTION

The novel rapid thermal process (RTP) reactor of this inventionprocesses not only a single semiconductor wafer, but also a plurality ofsemiconductor wafers. Herein, an RTP reactor is characterized by a shortprocess cycle time in comparison to the same process cycle time in aconventional reactor. The rapid heat-up of the wafer is one of the keysto the shorter process cycle times that characterize the reactor. TheRTP reactor, according to the invention, processes a multiplicity ofwafers or a single large wafer, e.g., 200 mm (8 inches), 250 mm (10inches), 300 mm (12 inches) diameter wafers, using either a single ordual heat source. (Hereafter, wafer sizes are indicated withoutexplicitly stating that the dimension given is the diameter of thewafer.)

According to one embodiment of the invention, 125 mm (5 inches) and 150mm (6 inches) wafers are processed three to a batch, and 200 mm (8inches), 250 mm (10 inches) and 300 mm (12 inches) wafers are processedindividually. However, larger batch sizes could be processed using alarger reactor that utilizes the principles of this invention.

Specifically, the semiconductor processing structure of this inventionhas a reaction chamber with a rotatable susceptor mounted within thereaction chamber. The rotatable susceptor has a first surface adaptedfor mounting one of (i) a single wafer and (ii) a plurality of wafersthereon and a second surface. A radiant heat source is mounted outsidethe reaction chamber so that the radiant heat from the heat sourcedirectly heats the wafer or wafers mounted on the rotatable susceptor.The radiant heat source raises the temperature of the wafer or wafers toa substantially uniform processing temperature, i.e., a temperaturesufficiently uniform so as to yield acceptable process results, in atime period such that the semiconductor processing structure ischaracterized as a rapid thermal process reactor.

In another embodiment, the semiconductor processing structure alsoincludes a heater mounted in the reaction chamber in proximity of thesecond surface of the rotatable susceptor. Preferably, the heater is aresistance heater. Power to the resistance heater is supplied by aninsulated electrical supply lines that have insulation that has atemperature rating that is less than a reaction chamber operatingtemperature. To thermally insulated the insulated electrical supplylines from the reaction chamber operating temperature, the lines arerouted through an annular shaft.

The annular shaft has a wall; a first end fixedly attached to theresistance heater; a second end; and a channel extending, in a directionperpendicular to the first and second ends, from the second end to thefirst end through the wall. The second end of the annular shaft isexterior to the reaction chamber. The insulated electrical supply linepasses through the channel to the resistance heater thereby thermallyinsulating the insulated electrical supply line from the reactionchamber operating temperature. In one embodiment, a screw, preferably amolybdenum screw, connects the insulated electrical supply line to theresistance heater.

In one embodiment of this invention, the rotatable susceptor is quartzand the first surface is bead blasted while the second surface is flamepolished. The susceptor has a pocket for each wafer that it supports.The pocket has a depth that is equal to or slightly less than thethickness of the wafer so that when the wafer is placed in the pocket, asurface of the wafer is parallel with or slightly higher than the firstsurface of the susceptor.

If a single wafer is being processed, the center of the pocket can beeither coincident with or offset from the center of the rotatablesusceptor. Offsetting the pocket facilitates loading and unloading ofthe wafer.

To enhance the uniform temperature of a wafer, a silicon carbide clothis placed in a pocket formed in the susceptor. This pocket typically hasa depth greater than the depth of the pocket described above. In thiscase, an insert having an outer edge surface and a maximum dimension,typically a diameter, less than a maximum dimension, also typically adiameter, of the pocket is placed in the pocket. Since the size of theinsert is less than the size of the pocket, upon placement of the insertinto the pocket, a uniform recess is formed between the outer edge ofthe insert and an outer edge of the pocket. A wafer surround ring isplaced in the recess formed.

In one embodiment, the wafer surround ring and the insert have the samedepth so that when the wafer is placed on the wafer surround ring andthe insert, a surface of the wafer is parallel with or slightly higherthan the first surface of the susceptor and the wafer is held in placeby the outer edge surface of the pocket. In another embodiment, thewafer surround ring has a notch formed in the upper surface of the wafersurround ring. The notch has a bottom surface substantially parallel toan upper surface of the wafer surround ring and an edge surface thatconnects the upper surface of the wafer surround ring and the bottomsurface of the notch. The bottom surface of the notch is aligned with anupper surface of the insert while the upper surface of the wafersurround ring is aligned with the first surface of the susceptor. Inthis case, the wafer rests on the upper surface of the insert and thebottom surface of the notch. The edge surface of the notch holds thewafer in place on the susceptor.

In yet another embodiment, the heater in the reaction chamber isreplaced by a passive heat distribution structure that is mounted inproximity of the second surface of the rotatable susceptor. The passiveheat distribution structure includes a silicon carbide cloth containedwithin a quartz structure. Alternatively, a graphite cloth can be used.

To inject process gasses into the reactor of this invention either aplurality of gas jets mounted in the reaction chamber or a center gasinjection head is used. The reaction chamber is bounded by vessel havinga water-cooled side wall, a water-cooled bottom wall, and aforced-air-cooled top wall. The forced-air-cooled top wall is a circulardomed-shaped quartz wall.

The radiant energy source of this invention includes a plurality of lampbanks where each lamp bank includes at least one lamp. The lamps arequartz-halogen lamps with a tungsten target.

The novel reactor of this invention also includes a susceptorpositioning mechanism coupled to the annular shaft and to a susceptorsupport means where the susceptor positioning mechanism moves theannular shaft and the susceptor support means in a first directionthereby moving the rotatable susceptor in the first direction.

In yet another embodiment of this invention, a reactor for processingsemiconductor wafers includes a reaction chamber vessel mounted in atable that has a top. A shell is movably connected to a track extendingin a first direction that is turn is rigidly affixed to the table. Acoupler means movably connects the shell to the track. The coupler meansincludes a plurality of connectors attached to the shell. The pluralityof connectors are selectively connectable to and disconnectable from theshell.

As the coupler means is moved along the track, the shell is moved in afirst direction from a first position contacting the table surface to asecond position removed from the table surface. Upon disconnecting oneof the plurality of connectors from the shell when the shell is in thesecond position, the shell is movable in a second directionsubstantially perpendicular to the first direction thereby allowingaccess, unrestricted by the shell, to the reaction chamber vessel.

In one embodiment, the coupler means has a yoke movably connected to thetrack. The yoke has first and second bosses, and third and fourthbosses. The first and second bosses each have a hole formed therein andthe center of the holes of the first and second bosses are on the sameaxis. The third and fourth bosses also each have a hole formed thereinand the center of the holes of the third and fourth bosses are on thesame axis. The shell has a first boss having a hole extendingtherethrough and a second boss having a hole extending therethrough.

A first pin extends through the hole in the first boss of the yoke, thehole in the first boss of the shell and the hole in the second boss ofthe yoke and connects the yoke to the shell. A second pin extendsthrough the hole in the third boss of the yoke, the hole in the secondboss of the shell and the hole in the fourth boss of the yoke andconnects the yoke to the shell. Upon removing the first pin, the shellcan be moved in the second direction.

As described above, the susceptor of this invention has a first surfaceadapted for mounting a semiconductor wafer thereon and a second surface.In one embodiment, the susceptor also has a plurality of openingsextending through the susceptor from the first surface to the secondsurface. A wafer support pin is contained in each of the susceptoropenings. When the wafer support pins are in a first position, the wafersupport pins are contained in the susceptor and in a second position,the wafer support pins hold the semiconductor wafer above the firstsurface. A plurality of supports, one for each wafer support pin, aremounted in the reactor so that when the susceptor is in a predeterminedposition, the plurality of supports engage the plurality of wafersupport pins and hold the wafer support pins in the second position.When the susceptor is in yet another predetermined position, theplurality of wafer support pins are in the first position.

The silicon deposits on the susceptor and quartz parts in the RTPreactor of this invention are etched using a method that includes:

flowing a gas having a predetermined percentage of HCL though the RTPreactor; and

reducing coolant flow to a wall of the RTP reactor so that the walltemperature is higher than a normal operating wall temperature for asilicon deposition process.

Particulate contamination in a reaction chamber of a rapid thermalprocess reactor having a susceptor that can be moved in a directionorthogonal to a surface of the susceptor is reduced by:

mounting the susceptor on a support means that extends through a wall ofthe reaction chamber;

moving the susceptor in the orthogonal direction by a mechanism attachedto the support means external to the reaction chamber thereby limitingthe number of parts within the reaction chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a simplified cross-sectional view of a prior art horizontalfurnace reactor.

FIG. 1B is a simplified orthogonal view of a prior art barrel reactor.

FIG. 1C is a simplified cross-sectional view of a prior art pancakereactor.

FIG. 2A is a simplified cross-sectional view of a rapid thermal processreactor according to one embodiment of the invention for processing amultiplicity of wafers.

FIG. 2B is a simplified cross-sectional view of a rapid thermal processreactor according to another embodiment of the invention for processinga multiplicity of wafers.

FIG. 2C is a simplified cross-sectional view of a rapid thermal processreactor according to another embodiment of the invention for processinga large single wafer.

FIG. 3A is a simplified cross-sectional view of a reactor according tothe invention in which wafers are heated with a single heat source andprocess gases are side-injected into the reaction chamber.

FIG. 3B is a simplified cross-sectional view of a reactor according tothe invention in which wafers are heated with a dual heat source andprocess gases are side-injected into the reaction chamber.

FIG. 3C is a simplified cross-sectional view of a reactor according tothe invention in which wafers are heated with a single heat source andprocess gases are center-injected into the reaction chamber.

FIG. 3D is a simplified cross-sectional view of a reactor according tothe invention in which wafers are heated with a dual heat source andprocess gases are center-injected into the reaction chamber.

FIG. 3E is a simplified cross-sectional view of a vessel including a topwall having an inflected or "bell" shape.

FIGS. 3F and 3G are a side view and top view, respectively, of asusceptor, according to another embodiment of the invention,illustrating another means of mounting a wafer on the susceptor.

FIG. 4A is a cross-sectional view of a reactor according to anotherembodiment of the invention taken along section 4B--4B of FIG. 4B.

FIG. 4B is a cross-sectional view of the reactor of FIG. 4A taken alongsection 4A--4A of FIG. 4A.

FIG. 4C is a simplified top view of the reactor of FIG. 4A.

FIGS. 5A and 5B are detailed views of a portion of FIGS. 4A and 4B,respectively.

FIG. 5C is a bottom view of the shell enclosing the bell jar of thereactor of FIGS. 4A to 4C, showing the interior portions of shell.

FIG. 5D is a top view of a portion of the reactor of FIGS. 4A to 4C,showing the reaction chamber and surrounding table.

FIGS. 5E and 5F are detailed views of a portion of FIG. 4B showing thesusceptor in a retracted and raised state, respectively.

FIG. 6 is a perspective view of two lamp banks of the reactor of FIGS.4A, 4B and 4C.

FIG. 7A is a cross-sectional view of a resistance heater for using witha reactor according to the invention.

FIG. 7B is a plan view of a section of the resistance heater of FIG. 7A.

FIG. 7C is a side cutaway view of the section shown in FIG. 7B.

FIG. 7D is a detailed view of a portion of the section shown in FIG. 7B.

FIG. 8 is a cross-sectional view illustrating a passive heatdistribution element for use with embodiments of the reactor of FIGS.4A, 4B and 4C in which a single heat source is used.

FIG. 9A is an exploded view of a gas injection head and structure forsupporting the gas injection head according to one embodiment of theinvention.

FIGS. 9B and 9C are a cross-sectional view and plan view, respectively,of an injector cone for use with the gas injection head of FIG. 9A.

FIGS. 9D and 9E are a cross-sectional view and plan view, respectively,of an injector hanger for use with the gas injection head of FIG. 9A.

FIGS. 9F and 9G are a cross-sectional view and plan view, respectively,of an injector umbrella for use with the gas injection head of FIG. 9A.

FIG. 10A is an exploded view of a gas injection head and structure forsupporting the gas injection head according to another embodiment of theinvention.

FIGS. 10B and 10C are a cross-sectional view and plan view,respectively, of an injection head for use with the gas injection headof FIG. 10A.

FIGS. 10D and 10E are a cross-sectional view and plan view,respectively, of an injection head top for use with the gas injectionhead of FIG. 10A.

FIG. 11 is an exploded view of a gas injection head and structure forsupporting the gas injection head according to another embodiment of theinvention.

FIG. 12 is a plan view of lamps used with a reactor according to anembodiment of the invention showing the position of the lamps relativeto the susceptor.

FIGS. 13A and 13B are a side view of an induction coil disposed beneatha susceptor according to an embodiment of the invention and a plan viewof the induction coil, respectively.

FIGS. 14A and 14B are a plan view and side view, respectively, of waferand wafer surround ring mounted in a pocket of a susceptor according toan embodiment of the invention.

FIG. 14C is a cross-sectional view of a wafer surround ring, cloth, andwafer mounted in a pocket of a susceptor according to another embodimentof the invention.

FIG. 14D is a cross-sectional view of a wafer surround ring and wafermounted in a pocket of a susceptor according to another embodiment ofthe invention.

FIG. 14E is a cross-sectional view of a wafer surround ring, cloth, andwafer mounted in a pocket of a susceptor according to another embodimentof the invention.

FIGS. 14F is a cross-sectional view of a wafer surround ring with arecess mounted in a pocket of a susceptor according to yet anotherembodiment of this invention.

FIGS. 14G is a cross-sectional view of a wafer surround ring with arecess mounted in a pocket of a susceptor with a susceptor cloth placedin the bottom of the pocket according to yet another embodiment of thisinvention.

FIGS. 15A, 15B, 15C, 15D and 15E are top views of susceptors for usewith a reactor according to the invention illustrating possible ways ofmounting a wafer or wafers on a susceptor.

FIG. 16 is a simplified view of a reactor according to the invention inwhich a single computer is used to control both the gas panel and thescrubber.

FIG. 17 is a top view of a cluster of reactors according to theinvention, each of which is used to perform a particular semiconductorprocess, arranged around a sealed chamber containing a robot whichtransfers wafers between a cassette room and a reactor, or between tworeactors.

DETAILED DESCRIPTION

According to the principles of this invention, a novel rapid thermalprocess (RTP) reactor processes not only a single semiconductor wafer,but also a plurality of semiconductor wafers. Herein, an RTP reactor isa reactor that has a process cycle time that is short compared to thesame process cycle time in a conventional reactor. The RTP reactor ofthis invention can heat the wafer or wafers at a rate between 10° C./secand 400° C./sec. The rapid heat-up of the wafer is one of the keys tothe shorter process cycle times that characterize the RTP reactor ofthis invention. The RTP reactor, according to the invention, processes amultiplicity of wafers or a single large wafer, e.g., 200 mm (8 inches),250 mm (10 inches), 300 or mm (12 inches) diameter wafer, using either asingle or dual heat source. (Hereafter, wafer sizes will be indicatedwithout explicitly stating that the dimension given is the diameter ofthe wafer.)

According to one embodiment of the invention, 125 mm (5 inches) and 150mm (6 inches) wafers are processed three to a batch, and 200 mm (8inches), 250 mm (10 inches) and 300 mm (12 inches) wafers are processedindividually. However, larger batch sizes could be processed using alarger reactor that utilizes the principles of this invention. Forinstance, in another embodiment of the invention, a RTP reactorprocesses 150 mm (6 inches) wafers in batches of four wafers, 200 mm (8inches) wafers in batches of three wafers and 300 mm (12 inches) wafersin batches of one wafer.

FIG. 2A is a simplified cross-sectional view of an RTP reactor 200,according to one embodiment of the invention, for processing amultiplicity of wafers 210. Wafers 210 are mounted on a susceptor 201supported by susceptor support 212. Susceptor position control 202rotates wafers 210 during processing and raises and lowers susceptor 201to various positions for loading and processing of wafers 210. Heatcontrol 203 controls a single heat source 204 that heats wafers 210 to asubstantially uniform temperature during processing. Gas flow control205 regulates flow of gases into reaction chamber 209 of reactor 200through inlet channel 206 and gas injection head 207 and exhausts gasesfrom reaction chamber 209 through outlet channel 208.

Herein, a "substantially uniform temperature" is a temperaturedistribution that yields process results of acceptable quality for theparticular process being performed. For example, in epitaxial processes,the temperature distribution must be sufficiently uniform to yieldwafers that meet at least industry standards for slip, thicknessuniformity, and resistivity uniformity. In fact, in the RTP reactor ofthis invention, the temperature uniformity is such that for epitaxialprocesses, the process results are better than industry standard, asdiscussed more completely below.

FIG. 2B is a simplified cross-sectional view of an RTP reactor 220,according to another embodiment of the invention, for processing amultiplicity of wafers 230. As in FIG. 2A, reactor 220 includes asusceptor 201, susceptor support 212, susceptor position control 202,heat control 203, heat source 204, gas flow control 205, inlet andoutlet channels 206 and 208, gas injection head 207 and reaction chamber209. Reactor 220 also includes a second heat source 224 that is alsocontrolled by heat control 203.

FIG. 2C is a simplified cross-sectional view of an RTP reactor 240according to another embodiment of the invention for processing a largesingle wafer 250. Wafer 250 is mounted on susceptor 241. The remainderof the components of reactor 240 are the same as in reactor 220. Inparticular, reactor 240 includes two heat sources 204 and. 224. WhileFIGS. 2A to 2C illustrate an RTP reactor with center gas injection, asexplained below, these RTP reactors can also use a plurality of jets forside gas injection.

In prior reactors used for simultaneously processing a multiplicity ofwafers or large single wafers, long heat-up, processing, and cool-downcycles are required. For instance, for a deposition process thatrequires heating to 1100° C., the total time for heat-up, processing andcool-down is typically 45-90 minutes. (In this disclosure, a depositionprocess is defined to include processes in which a film is grown on awafer.) For a similar process and temperature, RTP reactors 200, 220 and240 require a much shorter time for heat-up, processing, and cool-down,i.e., 2-15 minutes.

In reactors 200, 220 and 240, although the thermal mass of susceptor 201increases the heat-up and cool-down times relative to reactors in whichthere is not a susceptor, susceptor 201 minimizes temperaturedifferentials between the center and perimeter of each wafer in themultiplicities of wafers 210 or 230 (FIGS. 2A and 2B), or single wafer250 (FIG. 2C) and thereby enhances the steady-state temperatureuniformity across wafers 210, 230 or wafer 250, relative to prior artreactors, during processing of wafers 210, 230 or wafer 250. Moreover,as explained more completely below, the materials of susceptor 201 areselected to minimize adverse thermal effects associated with susceptor201.

Heat source 204 (FIGS. 2A and 2C) is a radiant energy heat source. Heatsource 224 (FIGS. 2B and 2C) is a resistance heater. Alternatively, inview of this disclosure, those skilled in the art can implement heatsource 224 of RTP reactors 220 or 240 as an RF heat source rather than aresistance heater.

In each of the embodiments of the invention shown in FIGS. 2A to 2C,heat source 204 (FIG. 2A), or heat sources 204 and 224 (FIGS. 2B and 2C)elevate the temperature of wafers 210, 230 or wafer 250 quickly from theambient temperature to the steady-state process temperature such thatthe temperature is substantially uniform throughout wafers 210, 230 orwafer 250, and maintain the substantially uniform temperature for theduration of the process. After processing, wafers 210, 230 or wafer 250are cooled by hydrogen gas and then nitrogen gas is used to purgereactant gases from reaction chamber 209. Quick heat-up allows wafers210, 230 or wafer 250 to be processed quickly. Substantially uniformwafer temperature is important for a number of semiconductor processes,such as in formation of an epitaxial layer where substantially uniformtemperature is critical in obtaining acceptably uniform thickness andresistivity.

An important aspect of the invention is that the number of components inreaction chamber 209 has been minimized. Specifically, the onlycomponents contained within reaction chamber 209 are susceptor 201,susceptor support 212, heat source 224 (if applicable) and gas injectionhead 207. Thus, potential sources of particulate contamination inreaction chamber 209 have been significantly reduced in comparison toprevious reactors which typically include all or part of susceptorposition control 202 within reaction chamber 209.

RTP reactors 200, 220 and 240 can be used to perform all of theprocesses performed by prior art RTP reactors, which processed onlysingle wafers of 200 mm (8 inches) or less. For example, RTP reactors200, 220 and 240 can be used for annealing or other semiconductorprocess steps in which no additional layers or conductivity regions areadded to a wafer.

For example, an anneal time of about two seconds at a temperature ofabout 1100° C. fully activates and removes damage from about a 10¹⁶ iondose of arsenic implanted at about 80 keV. Typically, rapid thermalanneals using reactors 200, 220 and 240 last a few seconds, in the rangeof from about one second to about 15 seconds, and have peak temperaturesranging from about 800° C. to about 1200° C. The fraction of dopantactivated typically ranges from about 50% to about 90%. As is known tothose skilled in the art, the particular time and peak temperaturedepends on the implant dose and species.

In addition to annealing, RTP reactors 200, 220 and 240 can sinter metalcontacts. To achieve a good metal-to-semiconductor contact afterdeposition, any one of RTP reactors 200, 220 and 240 heats themetal-semiconductor combination to a temperature at which someinterdiffusion and alloying occurs at the metal-semiconductor interface.For example, for aluminum, the temperature is typically in the range ofabout 450° C. to about 500° C. in either an inert or hydrogen atmospherefor a time in the range of about 5 seconds to about 20 seconds.

Alternatively, RTP reactors 200, 220 and 240 can be used to formsilicide-silicon ohmic contacts. In this application, a thin layer ofmetal, usually a refractory metal, is deposited over the wafer and thewafer is heated in one of RTP reactors 200, 220 and 240 to form a metalsilicide where the metal contacts the silicon. The unreacted metal isthen etched away. The formation of the metal silicide is notparticularly sensitive to either the temperature or time intervals usedin the heating step. For refractory metal silicides, the temperatureranges from about 800° C. to about 1100° C. and the time varies fromabout 1 to about 80 seconds.

The previous processes only used RTP reactors 200, 220 and 240 to heat asemiconductor wafer with a particular layer or layers. RTP reactors 200,220 and 240 can also be used to form a particular layer on a support,e.g., an oxide layer on a silicon wafer, various insulating, dielectric,and passivation layers on a silicon wafer or compound semiconductorwafer, or an epitaxial layer on a silicon wafer. RTP reactors 200, 220,240 can be used for compound semiconductor processing in a temperaturerange of 300°-600° C. RTP reactors 200, 220, 240 can also be used in theproduction of flat panel displays.

In addition, in view of this disclosure, those skilled in the art canuse RTP reactors 200, 220 and 240 for chemical vapor depositionprocesses such as growth of polysilicon.

For instance, a silicon epitaxial layer can be formed on the surface ofa silicon wafer. The wafers are heated to a temperature between 1000°and 1200° C. and exposed to a gaseous mixture consisting of a hydrogencarrier gas mixed with one or more reactive gases such as a siliconsource gas or dopant source gas. A layer of silicon is deposited on thesilicon substrate having the same crystal orientation as the substrate.

Below, individual aspects of the invention are described in greaterdetail. These descriptions are sometimes made with respect to theprocessing of single wafer batches and sometimes with respect toprocessing of multiple wafer batches. However, it is to be understoodthat in each of the descriptions below, one or more wafers can beprocessed in a single batch. Generally, the invention encompasses theprocessing of one or more wafers at a single time. Further, whilereference may be made below to particular batch sizes for wafers of aparticular size, it is to be understood that the invention encompassesbatch sizes other than those given. Generally, the invention is notlimited to the processing of any particular batch size for a given wafersize, nor is the invention limited to processing of wafers of particularsizes.

FIGS. 3A, 3B, 3C and 3D are simplified cross-sectional views of RTPreactors 300, 320, 340 and 360 according to the invention. These Figuresillustrate the basic elements of a reactor according to the invention,and illustrate several possible combinations of heat source and gasinjection system for a reactor according to the invention.

FIG. 3A is a simplified cross-sectional view of RTP reactor 300 forprocessing one or more semiconductor wafers, e.g., wafers 311, 312.Reactor 300 includes vessel 301, susceptor 302, susceptor support 304,radiant heat source 310 (including a plurality of lamps 305 andreflectors 306), passive heat distribution element 307, side inject gasjets 314a, 314b and gas exhaust pipes 309a, 309b.

Vessel 301 is formed by bottom wall 301a, side wall 301b, and domed topwall 301c. Walls 301a, 301b and 301c bound reaction chamber 303. Bottomwall 301a and side wall 301b are made of stainless steel and lined withquartz. In one embodiment, bottom wall 301a is circular and side wall301b is cylindrical. Dome-shaped top wall 301c is made of quartz so thatrelatively little of the radiant energy from radiant heat source 310 isabsorbed by top wall 301c. Thus, the radiant energy passes through topwall 301c unimpeded to heat directly wafers 311, 312.

The shape of top wall 301c is chosen as a compromise between severalfactors. As top wall 301c is made increasingly flat, the possibilityincreases that top wall 301c may collapse when reaction chamber 303 isheld at a vacuum pressure, i.e., less than 100 torrs, for instance,during a reduced pressure BICMOS process. On the other hand, as thecurvature of top wall 301c is increased, radiant heat source 310 ismoved increasingly further away from wafers 311, 312, which, in turn,requires a greater energy output from radiant heat source 310 tomaintain a given temperature of wafers 311, 312. Additionally, as thecurvature of top wall 301c increases, the distance of top wall 301c fromwafers 311, 312 also increases so that the process gases have a longertime to heat up before they are deposited on wafers 311, 312. Thecurvature of top wall 301c can also affect the flow of the process gasesas they descend upon wafers 311, 312.

The exact shape of top wall 301c is empirically determined by testing anumber of different shapes and choosing one that yields a desiredcombination of the above-identified characteristics affected by theshape of top wall 301c. In FIGS. 3A, 3B, 3C and 3D, upper wall 301c hasa cross-sectional shape that forms an approximately circular arc. FIG.3E is a simplified cross-sectional view of a vessel 381 including a topwall 381a having an inflected or "bell" shape.

Wafers 311, 312 (FIG. 3A) are mounted on circular susceptor 302 withinreaction chamber 303. In one embodiment, each of wafers 311, 312 isplaced into a recess, sometimes referred to as a "pocket," in susceptor302. The depth of the recesses is chosen in one embodiment so that wafertop surfaces 311a, 312a are approximately level with surface 302a ofsusceptor 302. The diameter of the recesses is chosen so that asusceptor ring (described in more detail below), sometimes called "awafer surround ring," can fit into each recess around the correspondingwafer 311 or 312.

FIGS. 3F and 3G are a side view and top view, respectively, of susceptor382, according to another embodiment of the invention, illustratinganother means of mounting wafer 391 on susceptor 382. Rather than beingplaced in a recess, as are wafers 311, 312 in FIGS. 3A, 3B, 3C and 3D,wafer 391 is placed on the surface of susceptor 382 and laterally heldin place by posts 382a, 382b, 382c, 382d. Posts 382a, 382b, 382c, 382dare made of quartz. Alternatively, if susceptor 382 is made of graphite,as is the case in some embodiments of the invention described below,posts 382a, 382b, 382c, 382d can be made of graphite. Posts 382a, 382b,382c, 382d may be formed integrally with the rest of susceptor 382, orformed separately and attached to susceptor 382 by, for instance, acompression fit in corresponding holes formed in susceptor 382. Thoughfour posts 382a, 382b, 382c, 382d are shown, it is to be understood thatother numbers of posts could be used, e.g., three.

Susceptor support 304 (FIG. 3A) holds susceptor 302 at selectedpositions in reaction chamber 303. Susceptor support 304 is raised orlowered to vary the position of wafers 311, 312 in reaction chamber 303.In one embodiment, susceptor 302, and passive heat distribution element307 are positioned at a first location in a first direction (theoperating position) during heating of wafers 311, 312 in reactionchamber 303 and positioned at a second location in the first directiondifferent from the first location (the loading position) when wafers311, 312 are being removed from, or placed into, reaction chamber 303.

Susceptor 302 susceptor, support 304 and passive heat distributionelement 307 are shown in the loading position in FIGS. 3A, 3B, 3C and3D. Wafers 311, 312 are placed into and removed from reaction chamber303 by one of a robot and a wafer handling system (not shown) through adoor 313 formed in side wall 301b. The loading position is chosen toallow the robot or wafer handling system to easily extend into reactionchamber 303 and place wafers 311, 312 on susceptor 302.

As explained in more detail below, when susceptor 302 is in the loadingposition, pins (not shown) extend through corresponding holes formedthrough susceptor 302 to raise wafers 311, 312 above surface 302a. Anynumber of pins can be used to raise each wafer 311, 312, though at leastthree are desirable to stably support a wafer, e.g, wafer 311. It isalso generally desirable to minimize the number of pins used to minimizemechanical complexity. In one embodiment of the invention, three pins,located 120° apart in the radial direction around susceptor 302, areused to support 125 mm (5 inches), 150 mm (6 inches) and 200 mm (8inches) wafers, and four pins, located 90° apart, are used to support250 mm (10 inches) and 300 mm (12 inches) wafers.

Because wafers 311, 312 are raised above surface 302a, the robot orwafer handling arm does not contact surface 302a of susceptor 302 whenremoving wafers 311, 312, so scraping or other damage to surface 302a isavoided. Additionally, since wafers 311, 312 are raised above surface302a, the robot or wafer handling arm can remove wafers 311, 312 bysupporting wafer surfaces 311b and 312b, respectively, thereby avoidingdamage to surfaces 311a, 312a on which, in many processes for whichreactors 300, 320, 340 and 360 are used, a film has been deposited.

In FIG. 3A, after wafers 311, 312 are placed on susceptor 302, susceptor302, support 308 and passive heat distribution element 307 are raised tothe operating position so that wafers 311, 312 are nearer radiant heatsource 310, allowing radiant heat source 310 to more quickly andefficiently heat wafers 311, 312 during operation of reactor 300.

During operation of reactor 300, susceptor 302 is rotated, as describedmore completely below. The rotation of susceptor 302 varies, in a seconddirection that is orthogonal to the first direction, the position ofwafers 311, 312 within reaction chamber 303 while wafers 311, 312 arebeing processed. As a result, the process taking place within reactionchamber 303 is performed more uniformly since the varying position ofwafers 311, 312 substantially negates the effect of any non-uniformitiespresent in operation of reactor 300.

In the embodiments of the invention shown in FIGS. 3A and 3C, wafers311, 312 are heated by a single heat source: radiant heat source 310.Radiant heat source 310 includes a plurality of lamps 305 that emitradiant energy having a wavelength in the range of less than 1 μm toabout 500 μm, preferably in the range of less than 1 μm to about 10 μm,and most preferably less than 1 μm. A plurality of reflectors 306, onereflector 306 adjacent each lamp 305, reflect radiant energy towardwafers 311, 312.

Radiant heat source 310 is both water-cooled and forced-air cooled. Thecombination of water-cooling and forced-air cooling keeps lamps 305 andreflectors 306 within the required operating temperature range.

In reactors 300 (FIG. 3A) and 340 (FIG. 3C), passive heat distributionelement 307 is mounted beneath susceptor 302 in proximity to susceptor302. As used herein, "proximity" means as close as possible consideringthe limitations imposed by the physical space requirement for connectingsusceptor 302 to susceptor support 304. Passive heat distributionelement 307 minimizes heat losses from susceptor 302, which, in turn,minimizes heat losses from wafers 311, 312. Passive heat distributionelement 307 is preferably made of a material that either absorbs andre-radiates heat toward susceptor 302, or that reflects heat towardsusceptor 302.

FIG. 3B is a simplified cross-sectional view of RTP reactor 320 forprocessing one or more semiconductor wafers such as wafers 311, 312 OfFIG. 3A. Reactor 320 is similar to reactor 300 and like elements arenumbered with the same numerals in FIGS. 3A and 3B. In reactor 320, adual heat source is used to heat wafers 311, 312.

The second heat source, resistance heater 327, generates heat whencurrent is passed through resistance elements formed in resistanceheater 327. Susceptor 302 is typically made of a material such as quartzthat absorbs little heat so that most of the heat from resistance heater327 is transmitted to wafers 311, 312. Radiant heat source 310 andresistance heater 327 maintain a substantially uniform temperaturethroughout each of wafers 311, 312.

Since there is more surface area at the edges of wafers 311, 312 than atthe center of wafers 311, 312, heat is lost from wafers 311, 312 morereadily at the edges than at the center. Consequently, absent somecompensation, larger temperature gradients exist at the edges of wafers311, 312 than at the center of wafers 311, 312. These temperaturegradients are undesirable and produce lower yields in a number ofsemiconductor processes. For instance, in formation of an epitaxiallayer, high radial temperature gradients throughout the wafer can induceslip and detrimentally affect thickness and resistivity uniformity. Tominimize these radial temperature gradients, in reactors 300, 320, 340and 360, a thermally insulative susceptor ring (not shown) is placedaround each of wafers 311, 312.

At the beginning of a process in reactor 300 (FIG. 3A) or reactor 320(FIG. 3B), the power to lamps 305, and in reactor 320, the power toresistance heater 327, is increased so that the temperature of wafers311, 312 is rapidly increased. The temperature of wafers 311, 312 issensed by a pyrometer or thermocouples (not shown), as described in moredetail below. As the temperature of wafers 311, 312 approaches thedesired temperature, the power to separate groups of lamps 305 is variedso that a substantially uniform temperature is achieved throughout eachof wafers 311, 312.

After wafers 311, 312 are heated to the desired temperature, ifnecessary for the process for which reactor 300 or 320 is being used,gases are introduced into reaction chamber 303 through side inject gasjets 314a, 314b. The gases flow past wafers 311, 312, susceptor 302 and,in reactor 320, resistance heater 327, and are exhausted from reactionchamber 303 through exhaust pipes 309a, 309b formed in bottom wall 301a.

FIG. 3C is a simplified cross-sectional view of RTP reactor 340 forprocessing one or more semiconductor wafers such as wafers 311, 312 ofFIGS. 3A and 3B. Like reactor 300 (FIG. 3A), only heat source 310 isused to heat wafers 311, 312 in reactor 340. However, in reactor 340,rather than introducing gases into reaction chamber 303 through sideinject gas jets 314a, 314b, as in reactor 300, gases flow through gasinlet pipe 354a and are introduced into reaction chamber 303 through gasinjection head 354b. Like reactors 300 and 320 (FIG. 3B), in reactor340, gases are exhausted from reaction chamber 303 through exhaust pipes309a, 309b formed in bottom wall 301a.

FIG. 3D is a simplified cross-sectional view of RTP reactor 360 forprocessing one or more semiconductor wafers such as wafers 311, 312 ofFIGS. 3A, 3B and 3C. In reactor 360, wafers 311, 312 are heated with adual heat source including radiant heat source 310 and resistance heater327. Gases are introduced into reaction chamber 303 through gas inletpipe 354a and gas injection head 354b and exhausted through exhaustpipes 309a, 309b.

In a typical semiconductor process involving the use of gases to deposita layer of material on a semiconductor wafer, it is necessary to performseveral gas purge operations. When door 313 is opened to place wafers311, 312 into or take wafers 311, 312 out of reaction chamber 303, theair surrounding reactor 300, 320, 340 or 360 enters reaction chamber303. In particular, the oxygen present in the air must be removed fromreaction chamber 303 before processing wafers 311, 312. Nitrogen isintroduced into reaction chamber 303 through side inject gas jets 314a,314b or gas injection head 354b, depending on the reactor, to purgereaction chamber 303 of oxygen. Hydrogen is then introduced intoreaction chamber 303 to purge the nitrogen.

After introduction of the hydrogen, wafers 311, 312 are heated and theprocess gases are introduced into reaction chamber 303, as describedabove. After the process is complete, hydrogen is used to purge anyremaining process gases from reaction chamber 303. Nitrogen is then usedto purge the hydrogen. The hydrogen and nitrogen purge gases help coolwafers 311, 312. After the nitrogen purge, when wafers 311, 312 arecool, door 313 is opened and wafers 311, 312 removed.

For processes involving deposition of silicon at process temperaturesbetween approximately 900°-1200° C., wafers 311, 312 are not cooled toambient temperature, but rather are cooled to a temperature in the rangeof 300°-600° C., depending on the temperature to which wafers 311, 312are heated during the process. Typically, cool down time is 2-5 minutes.In one embodiment, wafers 311, 312 are cooled to approximately 450° C.and cool down time is approximately 2.5-3.5 minutes. For processesconducted at lower temperatures (i.e., below about 900° C.), wafers 311,312 are cooled to approximately 50% of the process temperature beforebeing removed from reaction chamber 303.

Since wafers 311, 312 are not cooled all the way to ambient temperature,time is saved during cool-down, thus increasing wafer throughput.Further, reaction chamber 303 may be heated during one or more of theabove-described pre-processing purge operations to decrease the lengthof time required to process successive batches of wafers.

Wafers 311, 312 must be cooled at least to a temperature that ensureshardening of wafers 311, 312 before removal from reaction chamber 303.Further, reaction chamber 303 must be cooled to a temperature thatminimizes the possibility of an explosion that may occur if somehydrogen remains within reaction chamber 303 when door 313 is opened toremove wafers 311, 312.

When reactors 300, 320, 340 or 360 are used for semiconductor processesin which gases are used to deposit a layer of material on a wafer, e.g.,an epitaxial layer, some deposition may also occur on parts of reactors300, 320, 340 or 360, e.g., walls 301a, 301b, 301c, over time. Asexplained in more detail below, bottom wall 301a and side wall 301b arewater-cooled. Top wall 301c is cooled by the same air cooling used tocool lamps 305 and reflectors 306. Cooling of walls 301a, 301b, 301chelps minimize the undesirable growth of deposits on walls 301a, 301b,301c during deposition processes.

In conventional reactors, a "high etch" can be used to remove depositedsilicon from some parts of the reactor, for instance, those parts madeof graphite, by injecting a gas mixture that is at least 90% HCl intoreaction chamber 303 for 3-20 minutes when reaction chamber 303 is at atemperature of 1150°-1200° C. However, the high etch does not removesilicon deposits from quartz. Therefore, to clean quartz components inconventional reactors, the quartz components must be removed from thereactor. According to the principles of this invention, the depositedsilicon can also be removed from quartz components during the high etchby elevating the temperature of walls 301a, 301b to a temperature abovethe normal operating temperature. This can be done by allowing thetemperature of the fluid used to cool walls 301a, 301b during the highetch to rise so that walls 301a, 301b are cooled less effectively.

In reactors 300, 320, 340 and 360, only wafers 311, 312, susceptor 302,part of susceptor support 304, resistance heater 327 (in reactors 320and 360) or passive heat distribution element 307 (in reactors 300 and340), side inject gas jets 314a, 314b (in reactors 300 and 340) or gasinjection head 354b and part of gas inlet pine 354a (in reactors 320 and360) are disposed within reaction chamber 303. Prior art reactorstypically include a greater number of mechanical components inside thereaction chamber than the number found in reactors 300, 320, 340 and360. Contamination from these mechanical components (including materialdeposited during previous depositions) is a large source of particulatecontamination in prior art reactors. Since reactors 300, 320, 340 and360 have fewer mechanical components than in previous reactors,particulate contamination is less of a problem in reactors 300, 320, 340and 360, both because there are fewer mechanical components which mayprovide their own contaminants and because there are fewer mechanicalcomponents on which undesirable deposition may occur during repeated useof reactor 300, 320, 340 and 360. Thus, the presence of a relativelysmall number of mechanical components inside reaction chamber 303 ofreactors 300, 320, 340 and 360 is a substantial improvement overprevious reactors.

Additionally, since a substantially uniform temperature is maintainedover a larger region of reaction chamber 303 than in previous RTPreactors by the novel combination of heat source(s) and susceptor, it ispossible to process either a plurality of wafers or a single large wafer(e.g., 200 mm, 300 mm), rather than a single small wafer (e.g., 100 mm,125 mm, 150 mm) as done in previous RTP reactors. The ability to processa plurality of wafers significantly increases wafer throughput evenfurther, and the ability to process large wafers allows RTP reactors tokeep pace with the industry trend to larger wafers.

Reactors 300, 320, 340 and 360 also provide good reproducibility oftemperature from batch to batch over a large number of batches. As aresult, it is not necessary to recalibrate reactors 300, 320, 340 and360 often, relative to previous RTP reactors, to maintain the desiredtemperature uniformity. Since there is less downtime for calibration,wafer throughput is increased as compared to previous RTP reactorsbecause a greater percentage of time can be spent processing wafers.

Further, as compared to conventional reactors, multiple wafer batchescan be processed that have improved thickness and resistivityuniformity. Conventional reactors typically yield processed wafershaving thickness and resistivity variations of 3-10%. In the RTP reactoraccording to the invention, thickness variations of 1-2% and resistivityvariations of 1-5% are achievable.

FIGS. 4A and 4B are more detailed cross-sectional views of reactor 400of this invention. FIG. 4C is a simplified top view of reactor 400. Thecross-sectional view shown in FIG. 4A is taken along section 4B--4B ofFIG. 4B. The cross-sectional view shown in FIG. 4B is taken alongsection 4A--4A of FIG. 4A.

In the following description of reactor 400 (particularly with respectto FIGS. 4A, 4B, 4C, 5A, 5B, 5C, 5D, 5E and 5F), some elements(hereinafter, "missing elements") of reactor 400 do not appear incertain drawings though, in reality, the missing elements exist andshould appear. The missing elements have been eliminated from thedrawings for clarity. Missing elements not shown in one drawing mayappear in another drawing and one skilled in the art will be able toappreciate from the drawings, taken as a whole, how the missing elementswould appear and interrelate with illustrated elements in the drawingsin which the missing elements do not appear.

Frame 450 encloses selected parts of reactor 400, as discussed in moredetail below, and is made of, for instance, cold rolled 1018 steel. Asseen in FIG. 4C, reactor 400 is divided into several sections 400a,400b, 400c, 400d, 400e. Section 400a houses vessel 401, the heatsources, gas injection system, and the susceptor support and movementmechanisms. Section 400b houses a gas panel, if necessary for theprocess for which reactor 400 is used, that is equivalent in capabilityto gas panels used with prior art barrel CVD reactors. The gas panel isconfigured, of course, to support and provide all of the gases necessaryfor the processes to be performed in reactor 400. Section 400c housesparts of the gas exhaust system. Section 400d houses the power supplyand silicon controlled rectifiers used to drive the heat sources.Section 400e houses the remaining electronics: additional powersupplies, a computer for controlling process variables (e.g., gas flows,energy from heat sources), electrical relays, etc.

As seen in FIGS. 4A and 4B, section 400a is divided into two parts bytable 451. Shell 452 is mounted such that it contacts table 451,enclosing an upper portion of vessel 401 and lamp banks 405a, 405b (FIG.4A) and 405c, 405d (FIG. 4B). As seen in FIG. 4B, shell 452 is mountedto yoke 453 which is made of, for instance, 356 aluminum alloy. Yoke 453is movably mounted to linear rail 454. Linear rail 454 is available fromSchneeberger Inc. of San Francisco, Calif. as part no. 1 MRA 25658-W1-G3-V1. Yoke 453 slides up and down linear rail 454 to raise andlower shell 452 with respect to table 451. Linear rail 454 is attachedto column 458 which is made of, for example, 0.125 inch (3.18 mm) thickcold rolled steel. Column 458 is mounted on table 451.

During operation of reactor 400, shell 452 is lowered into the positionshown in FIGS. 4A and 4B, i.e., so that shell 452 contacts table 451.When it is desired to perform maintenance on reactor 400, shell 452 israised away from table 451 to allow access to components of reactor 400housed between shell 452 and table 451. Further, as explained in moredetail below, shell 452 may be pivoted with respect to yoke 453 aboutone of two pins 457a, 457b (FIG. 4B) so that shell 452 is not directlyabove table 451, thus making access to components of reactor 400 eveneasier.

Shell 452 performs various functions in reactor 400. Lamp banks 405a,405b, 405c, 405d are supported by shell 452. Further, shell 452 isformed, as described below, with passages for routing air to providecooling of lamp banks 405a, 405b, 405c, 405d and the upper portion ofvessel 401. When center injection of process gases is utilized (see,e.g., FIGS. 3C and 3D), shell 452 also houses gas inlet tube 408a andother hardware used in the gas distribution system, as well as coolingwater tubing through which cooling water flows to cool lamp banks 405a,405b, 405c, 405d. Finally, shell 452 protects vessel 401 from damage.

Shell 452 is made of aluminum and coated with high temperature teflonpaint. The teflon paint helps shell 452 withstand the high temperaturesto which shell 452 is subjected during processing of wafers in reactor400.

Vessel 401 has three walls: bottom wall 401a, side wall 401b, and upperwall 401c. The region inside vessel 401 constitutes reaction chamber403. Top wall 401c has an approximately circular arc and is 0.197 inches(5 mm) thick. The topmost point of the inner surface of top wall 401c isapproximately 4.619 inches (11.73 cm) from the surface of table 451 thatcontacts shell 452. Wafers (not shown) are put into and taken out ofreaction chamber 403 through door 413 (FIG. 4A) formed in side wall401b. The wafers are placed into recesses formed in susceptor 402, asdescribed more completely below. The distance between susceptor 402 andside wall 401b is about 1.5 inches (3.8 cm).

In FIGS. 2A-2C above, showing simplified cross-sectional views ofvarious reactors 200, 220 and 240 according to the invention, susceptorposition control 202 rotated, raised, and lowered susceptor 201. InFIGS. 4A and 4B, this susceptor position control includes, in reactor400, motors 415 and 417. Motor 415 drives shaft 416 so that susceptor402 is rotated. Motor 417 drives belt 418 which, in turn, rotates leadscrew 428 so that plate 426 is raised and lowered, moving susceptor 402up and down. The vertical movement of susceptor 402 allows susceptor 402to be positioned at appropriate heights for loading and unloading of awafer or wafers, and processing of a wafer or wafers. Further, asdescribed in more detail below, when susceptor 402 is lowered to thewafer loading position, pins extend through holes in susceptor 402 tolift the wafer or wafers above susceptor 402 to enable easy unloadingand loading of the wafer or wafers.

Resistance heater 407 or, alternatively, a passive heat distributionelement (described in more detail below) is mounted on graphite annularshaft 419. Shaft 416 is mounted coaxially within annular shaft 419.Bellows assembly 420 (described in more detail below with respect toFIGS. 4E and 4F) is mounted between plate 426 and bottom wall 401a toseal region 427 surrounding shaft 416, annular shaft 419 and associatedmechanisms so that gases that might leak from reaction chamber 403through gaps between shaft 416 and annular shaft 419, and betweenannular shaft 419 and bottom wall 401a are contained. These gases arepurged as explained in more detail below.

In embodiments of the invention using a dual heat source, e.g., reactors220 and 240 of FIGS. 2B and 2C, respectively, lamp banks 405a, 405b,405c, 405d and resistance heater 407 are used to heat a wafer or wafersto a substantially uniform temperature. In embodiments of the inventionusing a single heat source, e.g., reactor 200 of FIG. 2A, only lampbanks 405a, 405b, 405c, 405d are used for heating; in these embodiments,a passive heat distribution element (described below with respect toFIG. 8) can be used to help achieve a substantially uniform temperaturethroughout the wafer or wafers.

As described in more detail below, in dual heat source embodiments ofthe invention, groups of lamps and resistance heater 407 are separatelyelectrically controlled to provide variable amounts of heat in responseto measurements of wafer temperature. In one embodiment, wafertemperature is not directly sensed, i.e., no temperature sensor contactsthe wafers. An optical pyrometer available from Ircon, Inc. of Niles,Ill., capable of measuring temperature in a range from 600° C. to 1250°C. is mounted in head 455 (FIG. 4B) outside shell 452. The pyrometerheat sensing element receives radiated heat from within shell 452through port 456a formed in shell 452. Port 456a is covered by a windowthat is typically made of thin quartz (BaF₂ or CaF₂). A second port 456bis formed in shell 452 so that a hand-held pyrometer can be used ifdesired. Port 456b can also be used to visually monitor what ishappening in reaction chamber 403 during operation of reactor 400. Thepyrometer is calibrated during test runs of reactor 400 by correlatingpyrometer measurements to temperature measurements of test wafers takenby a thermocouple that contacts the test wafers.

In addition to, or instead of, temperature measurement with a pyrometer,wafer temperature can be measured with thermocouple wire insertedthrough a port, e.g., port 425a (FIG. 4B), formed in vessel 401, asexplained in more detail below. As with the pyrometer, the thermocoupleis calibrated during test runs of reactor 400 by correlatingthermocouple measurements to temperature measurements of test waferstaken by another thermocouple that contacts the test wafers.

Walls 401a, 401b, 401c (FIGS. 4A and 4B) are maintained at a cooltemperature, e.g., 600° C., relative to the operating temperature ofreaction chamber 403. If walls 401a, 401b, 401c are not maintained atthis cool temperature, a film may be deposited on walls 401a, 401b, 401cduring any deposition process in reactor 400. Growth of a film on walls401a, 401b, 401c is detrimental for several reasons. During operation ofreactor 400, the film on walls 401a, 401b, 401c absorbs heat energywhich affects the heat distribution in reaction chamber 403 which canresult in unacceptable temperature gradients in the wafer. Additionally,the film on walls 401a, 401b, 401c may produce particulates duringoperation of reactor 400 that contaminate the wafer.

Bottom wall 401a and side wall 401b are cooled by a water flow passingthrough walls 401a and 401b, as described in more detail below. Lampbanks 405a, 405b, 405c, 405d are forced-air and water-cooled. Upper wall401c is forced-air-cooled. The forced-air is circulated by motor 422that drives two centrifugal blowers 423 (FIG. 4B). Only one blower isshown in FIG. 4B. The other blower is immediately behind the blowershown. Centrifugal blowers 423 are rated to pass 600 CFM of air at anoutlet pressure of 18 inches H₂ O. During operation of reactor 400, theflow rate through the cooling system is 600 CFM. Motor 422 and blowers423 that can be used with the invention are available from PaxtonProducts, Inc. of Santa Monica, Calif., part no. RM-87C/184TC.

Air that has absorbed heat from reaction chamber 403 or lamp banks 405a,405b, 405c, 405d is cooled to approximately 40°-100° C. by passingthrough a conventional heat exchanger 424 available as Part No. 725 fromEG&G Wakefield Engineering in Wake, Mass. Heat exchanger 424 is designedsuch that heat exchanger 424 cools the air by approximately 40° C. Thecooling water flow rate of heat exchanger 424 typically ranges from 6-10gallons per minute. The heated exhaust air is passed first throughblowers 423, and then through the heat exchanger 424. This order ispreferred since it provides better cooling than when the heated exhaustair was passed through heat exchanger 424, and then through blowers 423.

Process gases are supplied to reaction chamber 403 through gas inlettube 408a (FIG. 4B) and are injected into reaction chamber 403 throughgas injection head 414, which is described in more detail below.Alternatively, the gases flow through gas inlet tube 408b and areinjected into reaction chamber 403 through a plurality of gas injectionjets, e.g., gas injection jet 421a, inserted through ports, e.g., port425b, formed in bottom wall 401a, also described in more detail below.The gases flow past the wafers on susceptor 402 and are exhausted fromreaction chamber 403 through exhaust lines 409a, 409b to common exhaustline 409c (FIGS. 4A and 4B). Exhaust lines 409a, 409, 409c aremaintained at a pressure of approximately 1-5 inches of H₂ O below thepressure of reaction chamber 403 so that the gases are exhausted fromreaction chamber 403. The gases pass through exhaust line 409c tosection 400c of reactor 400 and are ultimately exhausted out of reactor400 in a conventional manner.

After being exhausted from reactor 400, the used reactant gases arecleaned by a scrubber (not shown) such as the scrubber described in U.S.Pat. No. 4,986,838, entitled "Inlet System for Gas Scrubber," issued toJohnsgard on Jan. 22, 1991, the pertinent disclosure of which is hereinincorporated by reference.

FIGS. 5A and 5B are views of a portion of FIGS. 4A and 4B, respectively,showing in detail shell 452 and components of reactor 400 between shell452 and table 451. FIG. 5C is a bottom view of shell 452 showing theinterior portions of shell 452. FIG. 5D is a top view of reactionchamber 403 and table 451 showing cooling air inlets 553a, 553b andcooling air outlets 554a, 554b. FIGS. 5E and 5F are views of a portionof FIG. 4B showing in detail a section of reactor 400 beneath table 451.FIG. 5E shows susceptor 402 in a retracted position for loading wafer511 onto susceptor 402 and FIG. 5F shows susceptor 402 in a raisedposition for processing wafer 511.

As shown in FIGS. 5A and 5B, lamp banks 405a, 405b, 405c, 405d are aboveupper wall 401c. Each lamp bank 405a, 405b, 405c, 405d includes one ormore lamps 505 and a like number of reflectors, one for each lamp 505,formed integrally as reflector assemblies 406a, 406b, 406c, 406d.(Herein, reference to a typical lamp or lamps is as lamp 505 or lamps505. One or more particular lamps are referred to as, for example, lamp505a.) Lamp banks 405a and 405b (FIG. 5A) each have seven lamps 505.Lamp banks 405c and 405d (FIG. 5B) each have one lamp 505. As explainedin more detail below, slots are formed in reflector assemblies 406a,406b, 406c, 406d, as shown, in part, in FIGS. 5A and 5B above lamps505a, 505b and 505d.

Lamp bank casings 535a, 535b, 535c, 535d enclose most of lamp bank 405a,405b, 405c, 405d, respectively. Lamp bank casings 535a, 535b, 535c, 535dare left open at the bottom, i.e., adjacent lamps 505, to allow radiantenergy from lamps 505 to pass to reaction chamber 403 and cooling air topass to vessel 401. Lamp bank casings 535a, 535b, 535c, 535d are madeof, for instance, gold-plated stainless steel.

Each lamp bank 405a, 405b, 405c, 405d is attached to shell 452 with fourstuds 504 that are threaded at each end. One threaded end of each stud504 screws into a mating threaded hole formed in shell 452. The otherend of each stud 504 screws into the corresponding lamp bank, e.g., lampbank 405a. In one embodiment, each lamp bank 405a, 405b, 405c, 405d ismounted such that corresponding mounting surfaces 515a, 515b, 515c, 515dform an angle of approximately 20° with susceptor 402. This angle can bevaried slightly for a particular lamp bank, e.g., lamp bank 405a, byappropriately adjusting the position of corners of lamp bank 405a usinga means explained in more detail below. This change in angularorientation is possible because of the spacing tolerance between thediameter of the threaded section of stud 504 and the threaded hole inlamp bank 405a.

It is to be understood that lamp banks 405a, 405b, 405c and 405d couldbe mounted at angular orientations other than 20°. In one embodiment ofthe invention, for the shape of upper wall 401c of reactor 400 shown inFIGS. 4A, 4B, 4C, 5A, 5B, 5E and 5F, each lamp bank 405a, 405b, 405c,405d is mounted such that corresponding mounting surfaces 515a, 515b,515c, 515d form an angle of between 10°-40° with susceptor 402. Otherangular ranges are appropriate for reactors according to the inventionhaving a vessel with a differently shaped upper wall.

FIG. 6 is a perspective view of lamp banks 405b and 405d. Each lampbank, e.g., lamp bank 405b, includes a lamp frame, e.g., lamp frames605b, 605d, a reflector assembly, e.g., reflector assemblies 406b, 406d,one or more lamps 505 (not shown in FIG. 6), and one or more sets oflamp clips 617. Each reflector assembly, e.g., reflector assembly 406b,is attached to a lamp bank, e.g., lamp bank 405b by nuts and bolts.Slots 618 are formed in each reflector of reflector assembly 406b toallow cooling air to pass through reflector assembly 406b and then pastlamps 505, as described in more detail below. Opposite ends of each lamp505 are attached to one of lamp clips 617, which are, in turn, attachedto lamp frame 605b with nuts and bolts.

Studs 504 are screwed into each of the four corners, e.g., corners 615a,615b, 615c, 615d, of a lamp frame, e.g, lamp frame 605b. A spacer, jamnut and nut (none of which are shown in FIG. 6) are threaded onto thethreaded end of each stud 504 that is screwed into lamp frame 605b. Thespacers can have different lengths so that the position of a lamp bank,e.g., lamp bank 405b, can be varied with respect to the shell 452 (FIGS.5A and 5B). In one embodiment of reactor 400, the centerline of theclosest lamps 505a, 505b, 505c, 505d is approximately 4.31 inches (10.95cm) from the surface of table 451 on which shell 452 is mounted, and thecenterline of the farthest lamps 505e, 505f is approximately 6.31 inches(16.0 cm) from the same surface of table 451. However, for a 20° angularorientation of lamp banks 405a, 405b, 405c, 405d, these distances can bevaried up or down approximately 2 inches (5.08 cm).

Power is routed from section 400d (FIG. 4C) of reactor 400 to lamps 505with high temperature wire. The high temperature wire is routed throughopenings 556a, 556b formed in table 451 (FIG. 5D). The wire for two lampbanks, e.g., lamp banks 405b, 405d, passes through one of openings 556a,556b and the wire for the other two lamp banks, e.g., lamp banks 405a,405c, passes through the other of openings 556a, 556b.

As shown in FIG. 6, the high temperature wire enters shell 452 throughmilitary connectors, e.g., military connectors 604a, 604b, mounted inrouting boards 610. (Only one routing board 610 is shown in FIG. 6;however, it is to be understood that there is a similar routing board610 associated with lamp banks 405a and 405c.) The high temperature wireis bound together in wire bundles, e.g., wire bundles 611a, 611b, withinshell 452. Wire bundle 611a includes the high temperature wires forlamps 505 in lamp bank 405b, and wire bundle 611b includes the hightemperature wires for lamps 505 in lamp bank 405d.

A spacer, jam nut, wire lug and nut, e.g., spacer 606a, jam nut 607a,wire lug 608a, nut 609a, are threaded onto each of a plurality ofscrews, e.g., screw 616a, that are screwed into lamp frame 605b. Thereis one screw for each lamp 505. Screw 616a makes electrical connectionfrom the corresponding lamp 505 through electrically insulative spacer606a (which, in one embodiment, is made of ceramic) to wire lug 608a. Anelectrically conductive wire 619a, one of the high temperature wires inwire bundle 611a, electrically connects wire lug 608a (and, thus, a lamp505) to military connector 604a and, eventually, to an external powersource.

As previously noted, lamp banks 405a, 405b, 405c, 405d are water-cooled.Cooling water supplied from an external water supply passes throughcopper tubing, e.g., tubing 612, attached to the back of each lamp bank405a, 405b, 405c, 405d. Tubing 612 is attached to routing board 610 withquick disconnects 613a, 613b. Cooling water is inlet through tubingsection 612a. The cooling water is routed through tubing 612 to the backof lamp bank 405b where, though not visible in FIG. 6, tubing 612 isrouted in a snake-like fashion across most of the back surface of lampbank 405b to achieve a large amount of water-cooling of lamp bank 405b.The cooling water then flows to tubing 612 on the back of lamp bank405d, then returns through tubing 612 to tubing section 612b to bereturned to the water drain of the external water supply. The coolingwater flow rate is, in one embodiment, approximately 1.5 gallons perminute.

Lamps 505 supply radiant energy to wafer 511 (FIGS. 5E and 5F) inreaction chamber 403 to heat wafer 511. Lamps 505 are, for instance,quartz halogen lamps. A voltage is applied to each of lamps 505,resulting in the heating of a tungsten filament to produce radiantenergy in a short wavelength range, i.e., in the range of less than 1 μmto about 500 μm. Quartz halogen lamps suitable for use with theinvention are sold by Ushio American, Inc. of Torrance, Calif. 90502 asmodel no. QIR 480-6000E. The specifications for these lamps are shown inTable 1.

                  TABLE 1                                                         ______________________________________                                        Specification for Radiant Energy Lamps 505                                                            Maximum  Maximum                                      Design                                                                              Design    Color   Overall  Light  Bulb                                  Volts Watts     Temp.   Length   Length Diameter                              (v)   (W)       (°K. )                                                                         (mm)     (mm)   (mm)                                  ______________________________________                                        480   6,000     3,150   300      248    11                                    ______________________________________                                    

Each lamp 505 is mounted in a parabolic, gold-plated, highly polishedreflector. Each reflector is formed with a parabolic cross-sectionalshape along the length of respective lamp 505. The reflectors areprovided to maximize the amount of heat transmitted to reaction chamber403, and thus to wafer 511. Radiant energy that is emitted from lamps505 in a direction away from reaction chamber 403 is redirected by thereflectors toward reaction chamber 403. Additionally, any energy that isreflected back from reaction chamber 403 is reflected by the reflectorstoward reaction chamber 403 again. Generally, the reflectors can haveany shape and orientation that does not result in limiting the life ofthe bulbs in lamps 505, or that does not result in an uneven temperaturedistribution in wafer 511.

As noted above, in reactor 400, all of the reflectors for each lamp bank405a, 405b, 405c, 405d are formed integrally as reflector assemblies406a, 406b, 406, 406d. Reflector assemblies 406a, 406b, 406c, 406d arecommercially available from Epitaxial Services located in Sunnyvale,Calif. Another reflector assembly suitable for use with this inventionis available from Vector Technology Group, Inc. of Santa Clara, Calif.under the name of Spiral-Array Reflector Extended (part number 5815).

In addition to reflector assemblies 406a, 406b, 406c, 406d, reflectors517 (FIGS. 5A and 5B) are mounted to clamp ring 401d with bolts.Reflectors 517 are made of sheet metal, e.g., stainless steel, and areplated with a reflective material such as gold, nickel or silver.Typically, the entire surface of reflectors 517 are plated, though it isonly necessary that the surface of reflectors 517 facing into reactionchamber 403 be plated. Reflectors 517 are attached around the entireperiphery of reaction chamber 403 and are positioned so as to reflectenergy toward susceptor 402.

Upper wall 401c is made of quartz so that relatively little of theradiant energy from lamps 505 is absorbed by upper wall 401c, allowingmost of the radiant energy to be transmitted through reaction chamber403 directly to wafer 511. As best seen in FIGS. 5E and 5F, upper wall401c is clamped in place by threaded member 549 which extends throughclamp ring 401d into a threaded hole formed in table 451. Clamp ring401d is made of stainless steel. Two O-rings 551a, 551b are placed ingrooves in table 451 so that when threaded member 459 is tightened down,O-rings 551a, 551b are compressed to form a seal between table 451 andupper wall 401c. A further seal between clamp ring 401d and upper wall401c is formed by O-ring 551c.

In addition to the water-cooling described above, lamps 505 andreflector assemblies 406a, 406b, 406c, 406d are cooled by a flow offorced-air. Referring to FIG. 5C, cool air enters a cavity formed in thetop of shell 452 through air inlets 553a, 553b. Air inlets 553a, 553bhave a diameter of 3 inches (7.6 cm). The cool air passes through sixvents 555a, 555b, 555c, 555d, 555e, 555f to the region between shell 452and vessel 401. As the air passes through the region between shell 452and vessel 401, the air passes over and cools reflector assemblies 406a,406b, 406c, 406d and lamps 505. The air then passes over upper wall 401cof vessel 401, cooling upper wall 401c.

Referring to FIG. 5D, the heated air exits the region between shell 452and vessel 401 through air outlets 554a, 554b formed in table 451. Airoutlets 554a, 554b have a diameter of 4 inches (10.2 cm). The heated airis then returned to the heat exchanger, as described above with respectto FIG. 4B, where the air is cooled. The cooled air is then recirculatedback to the region between shell 452 and vessel 401 to cool lamps 505,reflector assemblies 406a, 406b, 406c, 406d, and upper wall 401c again.

In embodiments of the invention using an RF heat source underneathsusceptor 402, as described in more detail below, the coil of the RFheat source is cooled by a flow of water through the coil that issupplied from below vessel 401.

As shown in FIG. 5D, table 451 has two sections. Table section 451a ismade of aluminum and table section 451b is made of 316 stainless steel.Stainless steel is used for table section 451b because of its goodresistance to corrosion and ability to withstand the high temperaturesto which table section 451b is subjected.

As noted above, shell 452 is mounted to yoke 453 (FIG. 4B) such thatshell 452 can be pivoted away from table 451 to either side of reactor400. As illustrated in detail in FIG. 5C, pins 457a and 457b areinserted through holes formed in mounting sections 552a, 552b (sometimesreferred to as "bosses") of shell 452 and matching holes formed in yoke453 (not shown in FIG. 5C) to hold shell 452 laterally in place withrespect to yoke 453. Shell 452 is held vertically in place by ends 453a,453b of yoke 453 (see FIG. 4B) that contact either end of mountingsections 552a, 552b of shell 452. Shell 452 is pivoted away from table451 by removing one of pins 457a, 457b and rotating shell 452 about theother of pins 457a, 457b. Since two pins 457a and 457b are provided,shell 452 may be opened in either of two directions so that access tovessel 401 and components of reactor 400 within shell 452 can be easilyaccomplished under a wide variety of conditions of use of reactor 400.

Side wall 401b and bottom wall 401a are shown in FIGS. 5E and 5F. Sidewall 401b and bottom wall 401a are both made of stainless steel and arewelded together. Quartz liners 501a and 501b are disposed in reactionchamber 403 adjacent bottom wall 401a and side wall 401b, respectively.Liners 501a and 501b protect bottom wall 401a and side wall 401b,respectively, from deposition of gases during processing of wafer 511 inreactor 400. Liners 501a, 501b are made of clear quartz having abead-blasted surface facing into reaction chamber 403. The bead-blastedsurface causes films deposited on liners 501a, 501b to stick to liners501a, 501b rather than to flake off as would otherwise be the case.Consequently, contamination that results from the flaking is avoidedand, after prolonged use of reactor 400, liners 501a and 501b can beremoved from reaction chamber 403 and cleaned by, for instance, an acidetch.

As seen in FIG. 5D, ports 425a, 425b, 425c, 425d are formed throughbottom wall 401a. Ports 425a, 425b, 425c, 425d each have a diameter of0.75 inches (1.9 cm). Ports 425a, 425b, 425c, 425d may be used forinserting a thermocouple into reaction chamber 403 to take temperaturemeasurements. Ports 425a, 425b, 425c, 425d may also be used forintroduction of additional purge gases into reaction chamber 403 duringpost-processing purging so as to cool wafer 511 faster. Ports 425a,425b, 425c, 425d may also be used to introduce jets of air against wafer511 before or during pre-processing or post-processing purging to helpprevent particulates from accumulating on wafer 511.

In one embodiment of the invention, thermocouple 525 (FIGS. 5E and 5F)is inserted through one of ports 425a, 425b, 425c, 425d (illustratively,port 425a). Thermocouple 525 includes thermocouple wire sheathed inquartz with the tip of the thermocouple wire left exposed. Thethermocouple wire may be, for instance, type K thermocouple wire. Thethermocouple wire is sheathed in quartz to impart stiffness so that theposition of the thermocouple wire may more easily be controlled withinreaction chamber 403, and to slow the degradation of the thermocouplewire that results from exposure to hydrogen present in reaction chamber403. The tip of the thermocouple wire may be capped with graphite tofurther protect the thermocouple wire from the hydrogen atmosphere inreaction chamber 403. The graphite is sufficiently thermally conductiveso that the temperature measurement capability of the thermocouple wireis not substantially inhibited.

Thermocouple 525 may be positioned at any desired height in reactionchamber 403 by moving thermocouple 525 up or down through port 525a. Inone embodiment, thermocouple 525 is positioned approximately 1 inch(2.54 cm) above the upper surface of susceptor 402. Additionally,thermocouple 525 may be rotated to any desired position. In oneembodiment of the invention, end 525a of thermocouple 525 is angled andthermocouple 525 rotated so that end 525a is closer to susceptor 402than would be the case where thermocouple 525 is straight.

FIG. 7A is a cross-sectional view of resistance heater 407, which ismade of three identical sections 707a, 707b, 707c, showing the patternof the resistance element. FIGS. 7B and 7C are a plan view and sidecutaway view, respectively, of section 707a of resistance heater 407.FIG. 7D is a detailed view of the portion of section 707a delineated bysection line A in FIG. 7B. Resistance heater 407 is made to order byUnion Carbide Advance Ceramics Corp. in Cleveland, Ohio, and can beobtained by presenting the drawings shown in FIGS. 7A, 7B, 7C and 7D,and specifying Part No. E10005.

The dimensions in FIG. 7D are defined in Table 2.

                  TABLE 2                                                         ______________________________________                                                         Dimension (inches                                                             unless otherwise                                             Ref. No.         indicated)                                                   ______________________________________                                        a                0.500                                                        b                0.250                                                        c                0.250                                                        d                0.433                                                        e                1.00 DIA                                                     f                0.563 R                                                      g                0.188 R                                                      h                0.359 DIA                                                                     0.200 DEEP                                                   i                0.234 DIA FARSIDE                                                             0.13 DEEP ONLY THIS                                                           HOLE                                                         j                60.0°                                                 k                0.125 R                                                      1                0.196 DIA THRU                                               ______________________________________                                    

Each section, e.g., section 707a, of resistance heater 407 is made ofthree layers: two outer layers of ceramic and an inner layer ofgraphite. FIG. 7A is a cross-sectional view of resistance heater 407showing the graphite layer. The graphite layer is patterned such thatelectrically insulative regions, e.g., region 708, separate portions ofthe graphite layer, e.g., portions 709a, 709b, so that the graphiteforms a maze-like path. Resistance heater 407 generates heat whencurrent is passed through this maze-like path. The electricallyinsulative regions, e.g., region 708, may be formed of, for instance,ceramic. Alternatively, the electrically insulative regions, e.g.,region 708, may be grooves formed in the graphite layer. In this lattercase, air in the grooves provides the necessary electrical insulation.

The diameter of resistance heater 407 is 14.0 inches (35.6 cm) and thethickness is 0.5 inches (1.27 cm). Resistance heater operates on 3-phasepower. At a voltage of 240 volts, 46 amps of current can be generated;at 480 volts, 92 amps of current can be generated.

Hole 710 is centrally formed in resistance heater 407 to allow shaft 516(FIGS. 5E and 5F) to pass through resistance heater 407 and supportsusceptor 402, as explained more fully below. A plurality of holes,e.g., holes 711a, 711b, are formed through resistance heater 407 toallow passage of mounting rods, e.g., mounting rods 512a, 512b (FIGS. 5Eand 5F), that are used in loading and unloading wafer 511, as describedmore in more detail below. Though twelve holes, e.g., holes 711a, 711b,are shown in resistance heater 407, it is to be understood that anynumber of holes may be formed to conform to a particular waferload/unload scheme. The holes, e.g., holes 711a, 711b, have a diameterof 0.375 inches (0.953 cm), i.e., slightly larger than the diameter ofmounting rods, e.g., mounting rods 512a, 512b. The holes, e.g., holes711a, 711b, are located to correspond to the locations of thecorresponding mounting rods, e.g., mounting rods 512a, 512b.

As seen in FIG. 7B and explained in more detail below, three molybdenumscrews 714a, 714b, 714c are disposed in section 707a of resistanceheater 407. Screw 714a provides electrical connection between anexternal electrical supply and the graphite resistance element withinsection 707a of resistance heater 407. Screws 714b and 714c are used tomake electrical connection between section 707a and sections 707b and707c, respectively. Returning to FIG. 7A, screw 714b of section 707a andscrew 714d of section 707b each make contact with sleeve 712 disposed inthe bottom ceramic layer of resistance heater 407, which is made ofmolybdenum or graphite, to form an electrical connection between thegraphite resistance elements in sections 707a and 707b. Similarconnections are made to connect sections 707a and 707c, and sections707b and 707c.

In FIG. 7B, the center of molybdenum screws 714b, 714c are each 6.614inches (16.80 cm) from the center of resistance heater 407 and 0.375inches (0.953 cm) from corresponding sides 717a and 717b, respectively,of section 707a. The center of molybdenum screw 714a is 0.813 inches(2.07 cm) from the center of resistance heater 407 and 0.407 inches(1.03 cm) from side 717a of section 707a. The diameter of the head ofeach molybdenum screw, e.g., screws 714a, 714b, 714c, is 0.359 inches(0.912 cm) and, referring to FIG. 7C, the thickness is 0.2 inches (0.508cm). An 0.125 inch (0.318 cm) thick slot 715 is formed adjacent thebottom of screw 714a through which electrical wire contacts screw 714aas described below. In reactor 400, surface 713 (FIG. 7C) is adjacentsusceptor 402.

As seen in FIGS. 5E and 5F, resistance heater 407 is mounted on quartzlayer 508 and covered with quartz cover 507. The surface of quartz cover507 facing susceptor 402 is located approximately 0.875 inches (2.22 cm)beneath the susceptor. Layer 508 protects resistance heater 407 fromdeposition of gases during processing of wafer 511. Cover 507 alsoprotects resistance heater 407 from deposition of gases. As with quartzliner 501 discussed above, after prolonged use of reactor 400, quartzlayer 508 and cover 507 can be removed from reaction chamber 403 andcleaned. Quartz layer 508 and cover 507 can be cleaned more easily thanresistance heater 407.

Additionally, since layer 508 and cover 507 are made of quartz, layer508 and cover 507 absorb relatively little of the heat transmitted fromresistance heater 407. Thus, cover 507 allows most of the heat fromresistance heater 407 to be transmitted to wafer 511, and layer 508 doesnot act as a heat sink that draws heat away from wafer 511.

Since resistance heater 407 is within reaction chamber 403, a highvoltage electrical supply must be routed into reaction chamber 403.However, during operation of reactor 400, the temperature withinreaction chamber 403 can reach approximately 1200° C. This elevatedtemperature exceeds the insulation temperature specification forcommercially available electrical wires. For example, in one embodimentof the invention, Firezone 101 electrical wire, commercially availablefrom Bay Associates of Redwood City, Calif. and rated for 399° C. and600 volts, is used to supply current to resistance heater 407. Further,for many processes, hydrogen is present within reaction chamber 403. Ifthe insulation on the wire fails, there is danger that electrical arcingin reaction chamber 403 may result in an explosion.

According to an embodiment of the invention, the electrical supplyproblems above are overcome by providing channels, e.g., channel 419a(FIGS. 5E and 5F) in annular shaft 419 that extend from the bottom ofresistance heater 407 out of reaction chamber 403. Channels, e.g.,channel 508a, are formed through quartz layer 508. Channel 508a connectsto channel 419a. Molybdenum screws, e.g., screw 524a, hold resistanceheater 407 to quartz layer 508. Screw 524a contacts the graphiteresistance elements of resistance heater 407 and extends into channel508a. Molybdenum was chosen as the material for screw 524a because ofits high electrical conductivity and good resistance to corrosion andheat (screw 524a can withstand temperatures up to 1370° C.).Electrically conductive wire, rated for a 400° C. environment, is routedfrom outside reaction chamber 403 through channels 419a and 508a toscrew 524a. In this manner, electric current is routed from outsidereaction chamber 403 through the resistance elements of resistanceheater 407 without exposing the electrical wire to a prohibitively hightemperature environment or a hydrogen atmosphere. Since resistanceheater 407 is supplied with three phase power, three sets of channelsand screws, as described above, are used to route the electrical supplyinto reaction chamber 403.

As described above, in some embodiments of the invention, only a singleradiant heat source above the reaction chamber is used. In thoseembodiments, it is desirable to put a layer of material below thesusceptor that re-radiates or reflects heat toward the wafer. Such apassive heat distribution element helps maintain substantially uniformtemperature throughout the wafers being processed.

FIG. 8 is a cross-sectional view of shaft 416 supporting susceptor 402on which wafer 511 is mounted. In one embodiment of reactor 400, cloth807 is sandwiched between cloth support 808 and cloth cover 809. Cloth807 can be made of, for instance, graphite, metal or silicon carbide. Inone embodiment of the invention, cloth 807 is silicon carbide. Cloth 807has the same diameter as susceptor 402, i.e., 14 inches (35.6 cm).

In one embodiment of the invention, cloth support 808 and cloth cover809 are quartz layer 508 and quartz cover 507, respectively, asdescribed above with respect to FIGS. 5E and 5F. Quartz layer 508 is0.625 inches (1.59 cm) thick and quartz cover is 0.125 inches (0.318 cm)thick. Quartz cover 507 extends just beyond the lower surface of quartzlayer 508 to better prevent particulates from contaminating cloth 807.However, quartz cover 507 should not extend so far that quartz cover 507hits bottom wall 401a when quartz cover 507, cloth 807 and quartz layer508 are lowered with susceptor 402 when wafer 511 is to be loaded orunloaded (FIG. 5E).

As noted above, bottom wall 401a and side wall 401b of vessel 401 arecooled by a water flow passing through walls 401a and 401b. As seen inFIGS. 5E and 5F, channels 503c are formed in bottom wall 401a and sidewall 401b is formed with cavity 503a. Both channels 503a and cavity 503ccontain baffles to direct the water flow so that bottom wall 401a andside wall 401b are cooled uniformly. Additionally, water flows in cavity503b formed in table 451 to cool O-rings 551a, 551b. Water is suppliedat a pressure of approximately 80 psi from an external water source tocavities 503a, 503b and channel 503c from beneath vessel 501 throughconventional piping, and the water flow rate is controlled by aconventional valve. In one embodiment of the invention, the water flowrate through each of channel 503c and cavities 503a, 503b isapproximately 1.3 gallons per minute.

When wafer 511 has been heated to a predetermined temperature, a gasmixture is introduced into reaction chamber 403 through one of twoconventional methods: center injection of the gases at the center ofdome-shaped upper wall 401c or side injection of the gases through sideports. A gas line connects the gas panel to a conventional T-valvelocated underneath table 451. The valve is used to switch between usingthe center injection method and the side injection method.

In the center injection method, gases pass through gas inlet tube 408a(FIG. 5B), and are injected into reaction chamber 403 through orificesformed in gas injection head 514 (FIGS. 5A and 5B) at a rate of 3-150slm, depending on the gases being used. Gas injection head 514 isdifferent from gas injection head 414 shown in FIG. 4B. Both gasinjection heads 414 and 514 are described in more detail below, as wellas an additional embodiment of a gas injection head for use with theinvention. In general, a gas injection head for use with the inventioncan have any of a number of shapes, e.g., shower head, conical, or ball.

Viewed from above vessel 401, gas injection head 514 is centrallylocated in vessel 401. Gas injection head 514 is held in place by anovel mounting method, as described in more detail below. Gas injectionhead 514 can be made from quartz or graphite. Graphite is used if it isdesired to preheat the gases as they enter reaction chamber 403. Gasinlet tube 408a is made of stainless steel and has a diameter of 0.25inches (0.64 cm). The gases pass down through reaction chamber 403, pastsusceptor 402 and resistance heater 407, and are exhausted from reactionchamber 403 through exhaust ports 409a and 409b (FIGS. 4A and 4B)located in bottom wall 401a.

FIGS. 9A-9G illustrate the construction of gas injection head 414. FIG.9A is an exploded view of gas injection head 414 illustrating theassembly of gas injection head 414 and structure for hanging gasinjection head 414 from gas inlet tube 408a. FIGS. 9B and 9C are across-sectional view and plan view, respectively, of injector cone 915.FIGS. 9D and 9E are a cross-sectional view and plan view, respectively,of injector hanger 915. FIGS. 9F and 9G are a cross-sectional view andplan view, respectively, of injector umbrella 916.

In FIG. 9A, gas inlet tube 408a is attached to stainless steel dome 908.Dome 908 fits over quartz ball 909, covering cavity 909a formed in ball909. An O-ring 912 provides a seal between dome 908 and ball 909.Indentation 914a is formed in gas injection head extension tube 914.Clamp 911 is a two-piece ring mounted around indentation 914a andinserted into cavity 909a such that clamp 911 rests on shelf 909b ofball 909. Clamp 911 is made of quartz. Clamp 911 is prevented fromcoming apart by the walls of cavity 909a. Because clamp 911 grips gasinjection head 414 and rests on shelf 909b, gas injection head 414 isheld in place at the desired height in reaction chamber 403. O-ring 913forms a seal between gas injection head 414 and dome 908.

Injector cone 915 (FIGS. 9B and 9C) is made of graphite and coated withsilicon carbide. In an alternative embodiment, injector cone 915 is madeof quartz. A single orifice 915b (FIG. 9B) is formed in peak 915a ofinjector cone 915. Four additional orifices 915c are formed on surface915e. Recess 915f is formed in injector cone 915 opposite peak 915a andis threaded. Lip 915d is formed at an inner end of recess 915f.

The dimensions in FIG. 9B are defined in Table 3.

                  TABLE 3                                                         ______________________________________                                                         Dimension (inches                                                             unless otherwise                                             Ref. No.         indicated)                                                   ______________________________________                                        b1                0.250                                                       b2                0.06 R                                                      b3                0.250 R                                                     b4                2.29                                                        b5                2.13                                                        b6                0.25 R                                                      b7                0.10                                                        b8                1.355                                                       b9                0.187                                                       b10               0.04 THREAD RELIEF                                          b11              90°                                                   ______________________________________                                    

The dimensions in FIG. 9C are defined in Table 4.

                  TABLE 4                                                         ______________________________________                                                         Dimension (inches                                                             unless otherwise                                             Ref. No.         indicated)                                                   ______________________________________                                        c1                2.250                                                                        16 THREAD                                                    c2                0.250                                                       c3                0.740 B.C.                                                  c4                0.035                                                       ______________________________________                                    

Injector hanger 916 (FIG. 9D and 9E) is made of graphite coated withsilicon carbide, is circumferentially threaded and has an outer diameterto match the diameter of recess 915f (FIG. 9B). Alternatively, injectorhanger 916 is made of quartz. Injector hanger 916 is formed with threespokes 916a (FIG. 9E) that extend inward from an outer ring 916b to aninner ring 916c. Hole 916d is formed through inner ring 916c throughwhich a gas injection head extension tube 914 extends to carries gasesfrom gas inlet tube 408a (FIG. 9A). Injector hanger 916 is screwed intorecess 915f of injector cone 915.

Injector umbrella 917 (FIGS. 9F and 9G) is made of fire-polished quartz.Surface 917a (FIG. 9F) of injector umbrella 917 contacts surface innerring 916c (FIG. 9E) of injector hanger 916. Gas injection head extensiontube 914 (FIG. 9A) extends through hole 917b formed in injector umbrella917.

The dimensions in FIG. 9D, 9F, and 9G are defined in Table 5.

                  TABLE 5                                                         ______________________________________                                                         Dimension (inches                                                             unless otherwise                                             Ref. No.         indicated)                                                   ______________________________________                                        d1                2.250 16 THREAD                                             d2                0.03 C                                                      e1                0.188 REF                                                   e2                0.878 REF                                                   e3                0.409 REF                                                   e4                0.650                                                       e5                0.400 + .010                                                                  -.000                                                       e6                1.355                                                       e7                0.125                                                       e8                0.13 R TYP                                                  e9               120.0°                                                f1                0.38 R                                                      f2                0.08 THK                                                    f3                0.45                                                        g1                3.41 DIA                                                    g2                0.400 DIA + 0.060                                                             -0.000                                                      ______________________________________                                    

As seen in FIG. 9A, when gas injection head 414 is used in reactor 400,gases pass through gas injection head extension tube 914 into cavity915g of injector cone 915. Some of the gases are discharged intoreaction chamber 403 through orifices 915b and 915c (FIGS. 9B and 9C).The remainder of the gas is discharged between spokes 916a of injectorhanger 916 (FIGS. 9A and 9E). Injector umbrella 917 (FIG. 9A) redirectsthis gas flow toward wafer 511 in reaction chamber 403.

Referring to FIG. 9A, gas injection head 414 is assembled in thefollowing manner. Gas injection head extension tube 914 is insertedthrough hole 916d (FIGS. 9D and 9E) in injector hanger 916 so thatinjector hanger 916 rests on lip 914b. Injector umbrella 917 is mountedaround gas injection head extension tube 914 adjacent injector hanger916. Injector cone 915 is screwed onto injector hanger 916. Gasinjection head extension tube 914 is then attached to gas inlet tube408a as described above.

FIGS. 10A-10E illustrate the construction of gas injection head 1014.FIG. 10A is an exploded view of gas injection head 1014 illustrating theassembly of gas injection head 1014 and structure for hanging gasinjection head 1014 from gas inlet tube 408a. Gas injection head 1014includes injector ball 1015, shown in FIGS. 10B and 10C, and injectorball top 1016, shown in FIGS. 10D and 10E.

The dimensions in FIG. 10B, 10C, 10D, and 10E are defined in Table 6.

                  TABLE 6                                                         ______________________________________                                                         Dimension (inches                                                             unless otherwise                                             Ref. No.         indicated)                                                   ______________________________________                                        B1                1.000                                                       B2                0.66 R                                                      B3                0.375 REF                                                   B4                0.50                                                        B5                0.75 R                                                      B6               60.0°                                                 B7               30.0°                                                 B8               30.0°                                                 B9                0.06                                                        B10               0.250                                                       B11               1.125                                                       B12               0.06 R                                                      C1                0.060                                                       C2                1.500                                                       C3                0.100                                                       D1                1.250                                                                        12 UNF-2B                                                    D2                0.09                                                        D3                1.00                                                        D4                0.02 C                                                      D5                0.06 R                                                      D6                0.04 C                                                      D7                0.250                                                       E1                0.400                                                       ______________________________________                                    

Injector ball 1015 and injector ball top 1016 are both made of graphitecoated with silicon carbide. Alternatively, injector ball 1015 andinjector ball top 1016 could be made of quartz. Eleven orifices 1015a(FIG. 10B) are formed through injector ball 1015 (FIGS. 10B and 10C).Other numbers of orifices could be used. Recess 1015b is formed ininjector ball 1015 and is threaded. Lip 1015c is formed at an inner endof recess 1015b.

Injector ball top 1016 (FIGS. 10A, 10D and 10E) is circumferentiallythreaded and has an outer diameter to match the diameter of recess1015c. Injector ball top 1016 is screwed into recess 1015b of injectorball 1015. Injector ball top 1016 has recess 1016a formed in the side ofinjector ball top 1016 that contacts lip 1015c. A hole is formed throughinjector ball top 1016 through which gas injection head extension tube914 extends and carries gases from gas inlet tube 408a (FIG. 10A).

As seen in FIG. 10A, when gas injection head 1014 is used in reactor400, gases pass through gas injection head extension tube 914 intocavity 1015d of injector ball 1015. The gases are discharged intoreaction chamber 403 through orifices 1015a.

Gas injection head 1014 is attached to gas inlet tube 408a in the samemanner as described above for gas injection head 414 (FIG. 9A).Referring to FIG. 10A, gas injection head 1014 is assembled in thefollowing manner. Gas injection head extension tube 914 is insertedthrough hole 1016b (FIGS. 10D and 10E) in injector ball top 1016 so thatinjector ball top 1016 rests on lip 914b. Injector ball 1015 is screwedonto injector ball top 1016. Gas injection head extension tube 914 isthen attached to gas inlet tube 408a as described above.

FIG. 11 is an exploded view of gas injection head 514 illustrating theassembly of gas injection head 514 and structure for hanging gasinjection head 514 from gas inlet tube 408a. Gas injection head 514 is ashower head 1115 formed integrally with gas injection head extensiontube 914. A plurality of orifices are formed through shower head 1115 tosurface 1115a. In one embodiment, 11 orifices are formed through showerhead 1115. When gas injection head 514 is used in reactor 400, gasespass through gas injection head extension tube 914 into cavity 1115b ofshower head 1115. The gases are discharged into reaction chamber 403through the orifices. Gas injection head extension tube 914 is attachedto gas inlet tube 408a in the same manner as described above for gasinjection head 414 (FIG. 9A).

In the side injection method, gases pass through gas inlet tube 408b(FIG. 5B) and are introduced into reaction chamber 403 through ports521a, 521b, 521c (FIG. 5D) formed in bottom wall 401a via a plurality ofgas injection jets, e.g., gas injection jet 421a (FIGS. 5E and 5F)arranged about the periphery of reaction chamber 403. (Hereafter, gasinjection jets are referred to generally as gas injection jets 421,though such a numerical designation does not appear in the Figures.)Viewed from above, ports 521a, 521b, 521c are formed symmetrically inbottom wall 401a, near the edge of bottom wall 401a and 120° apartradially. The centerline of each of ports 521a, 521b, 521c is 0.725inches (1.84 cm) from side wall 401b. The diameter of each of ports521a, 521b, 521c is 0.75-1.25 inches (1.9-3.2 cm). In one embodiment,the diameter of each of ports 521a, 521b, 521c is 0.875 inches (2.22 cm)Each of the gas injection jets 421, can be rotated and moved up and downthrough bottom wall 401a so that gases are expelled into reactionchamber 403 at various heights and/or orientations, as desired. The gasinjection jets 421 could enter reaction chamber 403 at other locationsif desired, e.g., through side wall 401b or upper wall 401c. Thelocation and direction of discharge of gases into reaction chamber 403is more important than the particular manner in which gas injection jets421 enter reaction chamber 403.

Gases are introduced into reaction chamber 403 through gas injectionjets 421 at flow rates of 10-200 slm, depending on the gases being used.In one embodiment, there are three gas injection jets 421, each of whichis made of quartz and has a single circular orifice with a diameter of0.180 inches (0.46 cm). It is to be understood that use of a differentnumber of gas injection jets 421 is within the ambit of the invention.For instance, 2-10 gas injection jets 421 can be advantageously used toaccomplish a desired gas flow through reaction chamber 403. Further, gasjets 421 may have more than orifice and the orifice shape may be otherthan circular. Additionally, gas injection jets 421 could be made ofstainless steel or graphite instead of quartz.

In one embodiment, gas injection jets 421 are oriented so that the gasflows from the gas injection jets 421 are directed to a point justbeneath upper wall 401c so that the gas flows collide, producing a gasflow that then descends over wafer 511 so that a uniform deposition isachieved. Alternatively, gas injection jets 421 may be oriented so thatthe gas flows are directed toward upper wall 401c and interact with thecurvature of upper wall 401c to produce yet another gas flow thatdescends over wafer 511. Since the gases travel the distance from gasinjection jets 421 to upper wall 401c and from upper wall 401c tosusceptor 402, the gases are well-heated by the time they reach wafer511. The gases flow down through reaction chamber 403, past susceptor402 and resistance heater 407 and are exhausted through exhaust ports509a and 509b.

During operation of reactor 400, gases may leak from reaction chamber403 through gaps between shaft 416 and annular shaft 419, and annularshaft 419 and bottom wall 401a (FIGS. 5E and 5F). This leakage isminimized as much as possible by making the distances between shaft 416and annular shaft 419, and annular shaft 419 and bottom wall 401a assmall as possible. The minimum spacing between shaft 416 and annularshaft 419 is approximately 0.062 inches (1.6 mm) in this embodiment. Thespacing between annular shaft 419 and bottom wall 401a is 0.031 inches(0.8 mm).

Additionally, as noted above, conventional bellows assembly 420,available as Part No. SK-1601-6009 from Metal Fab. Corp. in OrmondBeach, Fla., seals region 427 (see FIGS. 4A and 4B) surrounding shaft416, annular shaft 419 and associated mechanisms to contain leakinggases. Bellows assembly 420 has an accordion-like section 420b weldedbetween two flange sections (only upper flange section 420a is shown inFIGS. 5E and 5F). Section 420b is made of stainless steel sheet metaland compresses and expands as susceptor 402 is lowered and raised. Theflange sections, e.g., upper flange section 420a, are also made ofstainless steel. Upper flange section 420a is bolted to bottom wall401a. The lower flange section (not shown) is attached to shelf 426(FIG. 4B).

Bellows purge 526 purges gases from region 427. Purge gas is introducedinto region 427 through bellows purge 526 at a higher pressure than thepressure in reaction chamber 403. As a result, gases that wouldotherwise leak from reaction chamber 403 are forced back into reactionchamber 403. The purge gas also enters reaction chamber 403, but, sincethe purge gas enters the bottom of reaction chamber 403 through bottomwall 403a, and since the flow within reaction chamber 403 is downwardtoward exhaust lines 409a, 409b, the purge gas is quickly exhausted fromreaction chamber 403 through exhaust lines 409a, 409b. The remainder ofthe purge gas within region 427, and any process gases that may haveleaked into region 427, are discharged through exhaust tube 527. In oneembodiment, a vacuum pump draws a vacuum of approximately 10 torrthrough exhaust tube 527 to aid in removal of gases and particulatesfrom region 527. During processing of wafer 511 in reactor 400, hydrogenis used as a purge gas through bellows purge 526 since some of the purgegas enters reaction chamber 403. After processing of wafer 511, nitrogenis used as the purge gas.

As shown in FIGS. 5E and 5F, susceptor 402 is supported by shaft 516.The end of shaft 516 opposite the end attached to the underside ofsusceptor 402 is conically shaped and is inserted in and attached with apin (not shown) to a mating conically shaped recess formed in an end ofshaft 416. The fit between the conically shaped end of shaft 516 and theconically shaped recess of shaft 416 ensures that susceptor 402 remainslevel (i.e., does not wobble) when shaft 416 is rotated during operationof reactor 400. Maintenance of a level susceptor 402 is important toensure that layers of material that may be deposited on the wafer 511during operation of reactor 400 are deposited evenly over the surface ofthe wafer 511.

Alternatively, shaft 516 could have been formed with a cylindrical endrather than a conical end, and shaft 416 formed with a cylindricalmating hole if such a connection is found to minimize wobble ofsusceptor 402 as it rotates. The important point is that the connectionbetween shafts 416 and 516 be made so that susceptor 402 remains levelduring rotation of susceptor 402.

In an alternative embodiment, the end of shaft 516 inserted into shaft416 is cylindrical and has a hexagonal cross-section. A matinghexagonally shaped recess is formed in shaft 416. The weight ofsusceptor 402 holds shaft 516 in place in the recess formed in shaft416. The fit between the hexagonally shaped end of shaft 516 and thehexagonally shaped recess of shaft 416 ensures that susceptor 402 isproperly oriented with respect to the pins used to raise wafer 511 abovesusceptor 402 (described in more detail below) so that those pins willextend through the corresponding holes in susceptor 402. Alternatively,end 516a could have another cross-sectional shape, e.g., square, thatholds susceptor 402 in the proper orientation. End 516a also minimizeswobble of susceptor 402 to maintain the surface of susceptor 402supporting wafer 511 level during rotation of susceptor 402.

Shaft 516 can be made from, for instance, quartz, graphite or anyceramic material that can withstand the operating conditions (i.e., hightemperature, gaseous environment) within reaction chamber 403. In oneembodiment of the invention, shaft 516 is made of quartz. Quartz absorbsrelatively little heat, as compared to graphite, so that when shaft 516is made of quartz, there is less likelihood that shaft 516 will heat upand possibly cause temperature non-uniformity in wafer 511 mounted onsusceptor 402. Shaft 416 is made from, for instance, stainless steel.

It is desirable that the support for susceptor 402 be formed in twosections, i.e., shafts 416 and 516, because, in the preferred embodimentof the invention, shaft 516 is formed integrally with susceptor 402. Asdescribed below, it is desirable to use a different susceptor 402 toprocess wafers, e.g., wafer 511, of different sizes. Thus, the susceptorsupport must be formed with two shafts 416, 516 so that shaft 516 may beseparated easily from the remainder of the susceptor support when it isdesired to change to a different susceptor 402.

As part of processing wafer 511 with reactor 400, it is necessary toplace wafer 511 on susceptor 402 in reaction chamber 403 prior tobeginning the process, and remove processed wafer 511 from reactionchamber 403 after completion of the process. When it is desired toremove or insert wafer 511 from or into reaction chamber 403, susceptor402 is rotated to a particular position (denominated the "home"position) that allows removal of wafer 511. When wafer 511 is beingplaced onto, or removed from, susceptor 402, susceptor 402 is lowered toa position near bottom wall 401a.

FIG. 5E shows susceptor 402 in a lowered position in preparation forloading wafer 511 onto susceptor 402. A plurality of mounting rods,e.g., mounting rods 512a, 512b, are attached to bottom wall 401a. Themounting rods, e.g., mounting rod 512a are made of stainless steel orgraphite. Corresponding holes, e.g., holes 531a, 532a, and 533acorresponding to mounting rod 512a, are formed in resistance heater 407,quartz layer 508 and susceptor 402, respectively. Wafer support pins,e.g., wafer support pins 513a, 513b, are mounted in cylindrical recessesformed in the ends of the mounting rods, e.g., mounting rods 512a, 512bfor wafer support pins 513a, 513b, respectively. ((Hereafter, unlessreference is being made to a particular mounting rod, wafer support pinor corresponding hole, e.g., mounting rod 512a, the mounting rods, wafersupport pins and corresponding holes are referred to generally asmounting rods 512, wafer support pins 513 and holes 531, 532 and 533,though those numerical designations do not appear in the FIGS.) Whensusceptor 402 is in the position shown in FIG. 5E, mounting rods 512extend through holes 531, 532, 533 and engage wafer support pins 513 sothat wafer support pins 513 are raised above the surface of susceptor402 on which wafer 511 is to be mounted.

Door 413 (not shown in FIGS. 5E and 5F) is provided in one side ofvessel 401 through which wafer 511 is inserted into and removed fromreaction chamber 403. Wafer 511 may be placed on or removed fromsusceptor 402 either with a robotic system or with a manual mechanicalsystem. If the robotic system is used, the robot is programmed so thatthe robot arm extends the proper distance to pick up wafer 511 oraccurately place wafer 511 at a predetermined location on susceptor 402.If the manual system is used, mechanical stops are placed so as to limitthe motion of the wafer handling arm such that when the arm hits thestops, the arm is properly positioned to pick up or place wafer 511 fromor on susceptor 402. Thus, with either system, good control of thepositioning of wafer 511 on susceptor 402 is achieved.

Once wafer 511 is placed on wafer support pins 513, the wafer handlingarm is removed from reaction chamber 403 and door 413 is shut. Susceptor402 is raised to the position at which susceptor 402 is held duringprocessing of wafer 511 (FIG. 5F). As susceptor 402 is raised, mountingrods 512 withdraw through holes 531, 532, 533. Wafer support pins 513withdraw through holes 533. Eventually, wafer support pins 513 arewithdrawn so that tapered ends of wafer support pins 513 seat in thetapered sections of holes 533. At this point, wafer support pins 513 areflush with the surface of susceptor 402 on which wafer 511 is mounted sothat wafer 511 rests on susceptor 402.

Wafer support pins 513 are made of quartz so that wafer support pins 513do not absorb heat and create a hot spot within wafer 511. Wafer supportpins 513 must seat snugly in the tapered portion of holes 533 so thatreactant gases cannot flow into holes 533.

As described in more detail below, wafers of different sizes require adifferent susceptor 402 since, for each wafer size, the wafers arelocated at different locations on susceptor 402. Further, the number andlocation of mounting rods 512, wafer support pins 513, and holes 531,532, 533 varies with the particular susceptor 402 being used.Consequently, different mounting rods 512 are used to raise and lowerwafers of different sizes.

The locations of mounting rods 512 for each wafer size are shown in FIG.5D. For 125 mm (5 inch), 150 mm (6 inch) and 200 mm (8 inch), mountingrods 512b, 512d and 512e are used. Optionally, mounting rods 512a, 512b,512c and 512d can be used with 200 mm (8 inch) wafers. For 250 mm (10inch) wafers, mounting rods 512a, 512c, 512f and 512g are used. For 300mm (12 inch) wafers, mounting rods 512f, 512g, 512h and 512i are used.

As seen in FIGS. 5E and 5F, almost none of the susceptor supportstructure is exposed inside reaction chamber 403. Only a small portionof shaft 516 and a variable portion (depending on the position ofsusceptor 402) of annular shaft 419 are exposed inside reaction chamber403. The middle portion of shaft 516 is surrounded by quartz cover 507,which also serves to substantially seal shaft 416 and the bottom portionof shaft 516 from reaction chamber 403. Since resistance heater 407 israised or lowered with susceptor 402, this is true whether susceptor 402is in a lowered position as in FIG. 5E or a raised position as in FIG.5F.

Significantly, both motors 415 and 417 (FIGS. 4A and 4B) are outside ofreaction chamber 403. Since most of the components of the structure forsupporting and moving susceptor 402 are outside reaction chamber 403,there are relatively fewer surfaces on which process gases may beundesirably deposited, as compared to previous reactors. Thus, fewercontaminants are present during subsequent uses of reactor 400 that willdetrimentally affect the layer of material deposited on wafer 511 orthat may alter the heating characteristics of reactor 400.

As noted above, susceptor 402 can be rotated. Susceptor 402 can berotated in either the clockwise or counterclockwise directions. Therotation of susceptor 402 causes the position of each point on thesurface of wafer 511 (excepting a point coincident with the axis ofrotation of susceptor 402) to continually vary, relative to the meandirection of gas flow past wafer 511, during operation of reactor 400.Consequently, the effect of non-uniformities in heating or gasdistribution that would otherwise create non-uniformities in a filmdeposited on wafer 511, as well as dislocations and slip on wafer 511,are substantially negated. The rotation distributes the non-uniformitiesin heating or gas distribution over the upper surface 511a of wafer 511(FIG. 5F) rather than allowing them to be localized at a particularspot. Typically, susceptor 402 is rotated at a speed of 0.5-30 rpm. Theexact speed is determined empirically as part of the process of "tuning"reactor 400 after reactor 400 has been designated for a particularapplication.

As seen in FIGS. 5E and 5F, resistance heater 407 is attached to annularshaft 419 so that resistance heater 407 is a small distance beneathsusceptor 402. Though resistance heater 407 and susceptor 402 cannotcontact each other because the rotation of susceptor 402 would causeabrasion between susceptor 402 and resistance heater 407 that couldcreate undesirable particulates and possibly damage susceptor 402 orresistance heater 407, ideally, there would be minimal separationbetween resistance heater 407 and susceptor 402. In one embodiment,resistance heater 407 is approximately 0.5 inches (1.3 cm) beneathsusceptor 402. Since resistance heater 407 moves up and down withsusceptor 402 as susceptor 402 is moved up and down in reaction chamber403, resistance heater 407 provides, for a given power level, the sameamount of heat to wafer 511 independent of the position of susceptor 402within reaction chamber 403.

At the beginning of processing of wafer 511 in reactor 400, lamps 505and resistance heater 407 each supply heat such that the temperature ofwafer 511 is increased as quickly and uniformly as possible withoutproducing undue stresses in the wafer. Different amounts of heat can besupplied by each of lamps 505 and resistance heater 407. The amount ofheat supplied by each lamp 505 and resistance heater 407 ispre-determined based upon prior temperature calibration. When thetemperature within reactor 400 reaches a temperature within theoperating range of the reactor temperature sensor, e.g., thermocouple525, groups of lamps 505 and resistance heater 407 are separatelycontrolled, based upon the measured temperature within reactor 400, tosupply varying amounts of heat as necessary to maintain substantiallyuniform temperature throughout wafer 511 as wafer 511 is brought to theprocess temperature.

A plurality of silicon controlled rectifiers (SCRs) controls the currentsupplied to both heat sources and, thus, the amount of heat from each ofthe heat sources. In the embodiment of the invention shown in FIGS. 4A,4B, 5A, 5B, 5C, 5D, 5E and 5F, seven SCRs are used. SCRs 1 and 2 controlresistance heater 407. Since the amount of heat generated by resistanceheater 407 is directly proportional to the magnitude of the voltage andcurrent across the heating elements of resistance heater 407, SCRs 1 and2 change the current through the heating elements of resistance heater407 to increase or decrease the amount of heat supplied by resistanceheater 407. SCRs 3-7 each control a group of lamps 505. The radiantenergy from each lamp 505 is directly proportional to the voltage andcurrent applied to lamp 505. Therefore, each of the SCRs 3-7 controlsthe current to associated lamps 505 to modulate the amount of heatsupplied by those lamps 505.

FIG. 12 is a plan view of the layout of lamps 505. As previously noted,there are sixteen lamps 505, i.e., 505a, 505b, 505c, 505d, 505e, 505f,505g, 505h, 505i, 505j, 505k, 5051, 505m, 505n, 505o, 505p. The sixteenlamps 505 are formed in five groups. SCR 3 drives two side lamps 505aand 505b. SCR 4 drives four outermost lamps 505c, 505d, 505m and 505p inthe middle row of lamps 505. SCR 5 drives two centermost lamps 505e and505f in the middle row. SCR 6 drives lamps 505g, 505h, 505i and 505j,and SCR 7 drives lamps 505k, 505l, 505n and 505o.

According to the invention, lamps 505 may be connected in parallel or ina series/parallel combination. In the preferred embodiment of theinvention, all lamps 505 are connected in parallel and operated using a480 volt power supply. If, for instance, two lamps 505 were connected inseries, it would be necessary to use a 960 volt power supply to runlamps 505.

Control of lamps 505 and resistance heater 407 to modulate the amount ofheat supplied by each during operation of reactor 400 is performed by acomputer. The computer automatically controls each group of lamps 505and resistance heater according to parametric information stored in thecomputer and based upon previous temperature calibrations performed withreactor 400. The parametric information obtained from the calibrationruns is used by the computer to change the SCR and resistance heatercurrents to achieve the proper spatial and temporal heat distributionsnecessary to maintain substantially uniform temperature throughout wafer511 during the initial heating of wafer 511.

The computer control allows establishment of a number of different powerramp rates during initial heating of wafer 511. In one embodiment of theinvention, up to 30 different ramp rates can be used during initialheating by appropriately pre-programming the computer. The power ramprates used are determined empirically through a series of test runs ofreactor 400 so as to maintain substantially uniform temperature in wafer511 and, if appropriate to the process, minimize wafer slip.

When the temperature within reaction chamber 403 reaches a level atwhich the temperature sensor being used operates accurately (e.g.,800°-1100° C. if thermocouple 525 is used as the temperature sensor),the computer switches from the automatic control described above tofeedback control. The sensed temperature is monitored by the computerand used, along with stored parametric information about the lamps 505and resistance heater 407, to make appropriate adjustments to the SCRsand resistance heater 407 currents to appropriately control the heatoutput from lamps 505 and resistance heater 407 so as to maintain thetemperature distribution throughout wafer 511 within predeterminedlimits. The power to all lamps 505 is either increased or decreased asone; however, the ratio of power between lamps is fixed, so that anincrease in power to lamps 505 results in different amounts of increaseto individual groups of lamps according to the pre-determined (duringthe calibration runs) power ratios for the lamp groups.

A side view of the middle row of lamps 505 of FIG. 12 is seen in FIG.5A. Lamps 505 near the center of the row (and, thus, above the center ofthe susceptor 402), e.g., lamps 505e and 505f, are located further fromthe surface of susceptor 402 and, thus, the surface of wafer 511 (notshown in FIG. 12), than lamps 505 at either end of the row, e.g., lamps505c and 505d. Consequently, though it might be expected that lamps 505cand 505d are operated to supply more heat than lamps 505e and 505f sothat more heat is supplied to edge 511c (FIG. 5F) of wafer 511 tocounteract the known heat loss at the wafer edge 511c and maintainsubstantially uniform temperature throughout wafer 511, this is notnecessarily the case since the heat from lamps 505e and 505f musttraverse a greater distance, as compared to lamps 505c and 505d, beforebeing absorbed by wafer 511.

In embodiments of reactor 400 without resistance heater 407 andincluding cloth 807 (FIG. 8), during initial heating of wafer 511, lamps505a, 505b, 505c and 505d (FIGS. 5A and 5B) directed to edge 511c ofwafer 511 are controlled to radiate approximately 20-30% more energythan lamps 505e and 505f directed toward an area near the center ofwafer 511. As reaction chamber 403 approaches the process temperature,lamps 505a, 505b, 505c and 505d are controlled to radiate approximatelytwice as much energy as lamps 505e and 505f. The other lamps 505 arecontrolled to radiate an amount of energy between the energy levels oflamps 505a, 505b, 505c, 505d and lamps 505e, 505f. The exact amount ofenergy radiated by the other lamps 505 is determined empirically so asto minimize wafer slip and produce acceptably uniform resistivity. Theabove relationships between the amount of energy radiated by variousgroups of lamps has been found to yield substantially uniformtemperature throughout wafer 511 (or throughout each wafer when morethan one wafer is being processed) as wafer 511 is heated up.

In other embodiments of the invention including resistance heater 407(FIGS. 4A, 4B, 5E, 5F) instead of cloth 807, a similar relationshipbetween the radiated energies of particular lamps 505 exists. Theappropriate power ratios can be determined empirically by performingseveral calibration runs. It would be expected that centermost lamps505e, 505f would provide more energy relative to outermost lamps 505a,505b, 505c, 505d.

It is important to note that the lamp array shown in FIG. 12accommodates embodiments of the invention with or without resistanceheater 407. The lamp array remains the same in either embodiment; it isonly necessary to perform temperature calibration runs to ascertain theappropriate power ratios for the respective groups of lamps 505 so thatsubstantially uniform temperature is maintained throughout wafer 511.

Additionally, reactors according to the invention that are larger thanreactor 400 can utilize the same lamp array similar to the array shownin FIG. 12; again, it is only necessary to perform temperaturecalibration runs to determine the appropriate lamp power ratios toachieve substantially uniform wafer temperature. Such larger reactorscould be used to process larger wafers, or to process at one time morewafers of a given size, than is possible with reactor 400.

In an alternative embodiment of the invention, instead of usingresistance heater 407 underneath susceptor 402, a radio frequency (RF)heat source including an induction coil is disposed below susceptor 402.FIGS. 13A and 13B are a side view of induction coil 1311 disposedbeneath susceptor 402 according to an embodiment of the invention, and aplan view of induction coil 1311, respectively. Coil 1311 is woundsubstantially in a plane that is parallel to the plane of susceptor 402.As seen in FIG. 13A, the turns of coil 1311 have a variable distancefrom susceptor 402. At the edge of susceptor 402, the turns of coil 1311are relatively close to susceptor 402. Moving toward the center ofsusceptor 402, the turns of coil 1311 become relatively farther fromsusceptor 402. Near the center of susceptor 402, the turns of coil 1311become relatively close to susceptor 402 again.

Electric current is passed through coil 1311, inducing anelectromagnetic field in the vicinity of coil 1311. This electromagneticfield, in turn, induces an electric current in susceptor 402. Thiscurrent generates heat in susceptor 402. As is well known, the currentdistribution (and thus heat distribution) in susceptor 402 is a functionof the distance between turns of coil 1311, the distance between a giventurn of coil 1311 and susceptor 402, and the frequency of currentpassing through coil 1311. Therefore, these parameters are set so as toyield a desired temperature distribution in susceptor 402.

If an RF heat source is used, susceptor 402 must be graphite (ratherthan quartz) to absorb the energy from the electromagnetic field set upby the alternating current in coil 1311. Since graphite susceptor 402must absorb energy to heat wafer 511 mounted on susceptor 402, more timeis required to achieve a desired temperature level than is the case withthe combination of resistance heater 407 and quartz susceptor 402.

Reactor 400 may be used to process single wafers or a plurality ofwafers. Since the wafer or wafers to be processed are mounted in arecess in the susceptor, a different susceptor, e.g., susceptor 402, isrequired for each different wafer size since the number and size of therecesses are different. A different susceptor 402 is also requiredbecause of the different number of wafer support pins 513 (FIGS. 5E and5F) used to raise the different sizes of wafers above susceptor 402.Typically, this does not present a barrier to achieving high waferthroughput since batches of a particular wafer size are normallyprocessed one after the other, thus minimizing the number of susceptorchanges that are required. Each susceptor, e.g., susceptor 402 is 14inches (35.6 cm) in diameter and approximately 0.375-0.5 inches(0.95-1.27 cm) in thickness (other than at the location of the waferrecesses).

Susceptor 402 can be made of quartz. If susceptor 402 is made of quartz,the surface of susceptor 402 facing lamps 505 is bead blasted toincrease heat retention. The surface of susceptor 402 facing resistanceheater 407 or cloth 807 is made clear by, for instance, either flamepolishing or mechanical polishing, thus allowing more heat to passthrough susceptor 402 to wafer 511.

In the embodiment of the invention in which the heat source belowsusceptor 402 is resistance heater 407, susceptor 402 is preferably madeof quartz, which absorbs relatively little of the heat from resistanceheater 407. Most of the heat is transmitted through the quartz to wafer511, thus enabling the wafer or wafers to be heated relatively rapidly(on the order of 15-30 seconds).

In embodiments of the invention in which an RF heat source is usedbeneath susceptor 402, susceptor 402 must be made of graphite to absorbthe RF energy and generate heat that can be transmitted to wafer 511. Ifsusceptor 402 is made of graphite, susceptor 402 is coated with a thincoating of silicon carbide to prevent contamination of wafer 511 withcarbon as they sit on susceptor 402.

As has been noted several times, maintenance of a substantially uniformtemperature throughout wafer 511 is essential for accurate processing ofwafer 511. In particular, at the edge 511c of wafer 511, the heatdissipation from wafer 511 to the lower temperature ambient environmentwithin reaction chamber 403 may give rise to large temperature gradientsat the edge 511c which induce an undesirable phenomenon known as "slip"in epitaxial processing. Thus, there is a particular need for a means ofcontrolling the temperature at the edge 511c of wafer 511.

FIGS. 14A and 14B are a plan view and side view, respectively, ofsusceptor 402 on which wafer surround ring 1401 and wafer 1404 aremounted in pocket 1403 of susceptor 402 according to an embodiment ofthe invention. Wafer surround ring 1401 is mounted on spindle 1402 ofsusceptor 402. Spindle 1402 can be formed integrally with the remainderof susceptor 402 or spindle 1402 can be formed as a separate piece thatis dropped into pocket 1403. (Hereafter, in the following description ofthe invention, "spindle" is used to refer to an element that iscentrally located within pocket 1403 and can be formed integrally with,or separately from, susceptor 402. "Susceptor insert" is used to referto an element that is centrally located within pocket 1403 and can onlybe formed separately from susceptor 402. However, the terms denoteelements that are substantially similar, and the use of one or the otherterms may encompass formation of the element separately or integrallywith susceptor 402.) Wafer 1404 is mounted on top of wafer surround ring1401 and spindle 1402 such that the upper surface of wafer 1404 isrecessed slightly relative to wafer surround ring 1401.

Wafer surround ring 1401 is commercially available from MidlandMaterials Research of Midland, Mich. Wafer surround ring 1401 is made ofa material with relatively low thermal conductivity such as, forinstance, graphite or silicon carbide. Wafer surround ring 1401 has athickness 1401a of 0.125 inches (3.18 mm), a thickness 1401b of 0.10inches (2.54 mm) and a length 1401c of 0.60 inches (15.2 mm). Otherthicknesses 1401a, 1401b and lengths 1401c can be used. If graphite isused, wafer surround ring 1401 is coated with silicon carbide having athickness sufficient to prevent contamination of wafer 1404 with carbon.The exact thickness of the silicon carbide coating is proprietaryinformation of Midland Materials Research.

FIGS. 14C, 14D, 14E, 14F and 14G are cross-sectional views of additionalembodiments of a susceptor and wafer surround ring according to theinvention.

In FIG. 14C, susceptor cloth 1417, which can be made of, for instance,silicon carbide or graphite, is first placed into pocket 1403. Susceptorinsert 1412, which is made of quartz, is placed into the center ofpocket 1403 on top of susceptor cloth 1417 so that a recess is formedbetween outer edge 1450 of susceptor insert 1412 and outer edge 1451 ofpocket 1403. Wafer surround ring 1401 has a notch 1452 that has a bottomsurface 1453 and an edge surface 1454 that connects bottom surface 1453to top surface 1455. Bottom surface 1453 of wafer surround ring 1401 isaligned with a top surface 1456 of susceptor insert 1412. Top surface1455 of wafer surround ring 1401 is aligned with the top surface ofsusceptor 402. Wafer surround ring 1401, which is made of, for instance,silicon carbide or graphite, is placed into the recess within pocket1403 so that wafer surround ring 1401 surrounds susceptor insert 1412.Finally, wafer 1404 is placed on top of susceptor insert 1412 and intonotch 1452 of wafer surround ring 1401.

In FIG. 14D, wafer surround ring 1421 is placed around spindle 1422 inpocket 1403 of susceptor 402. Spindle 1422 can be made of, for instance,graphite or quartz. If spindle 1422 is made of graphite, spindle 1422can be formed integrally with the rest of susceptor 402, or spindle 1422can be formed as a separate piece and dropped into pocket 1403. Wafersurround ring 1421 is made of, for instance, silicon carbide orgraphite.

In FIG. 14E, susceptor-cloth 1437 is dropped into pocket 1403. Susceptorinsert 1432 is placed into the center of pocket 1403 on top of susceptorcloth 1437. Wafer surround ring 1421 is placed into pocket 1403 so thatwafer surround ring 1421 surrounds susceptor insert 1432 and susceptorcloth 1437. Finally, wafer 1404 is placed on top of susceptor insert1412 into the recess formed by wafer surround ring 1421. Susceptor cloth1437 and susceptor insert 1432 are made of the same materials assusceptor cloth 1417 and susceptor insert 1412.

In FIG. 14F, wafer surround ring 1441 is placed into pocket 1403. Wafer1404 is placed into a recess formed in wafer surround ring 1441. Wafersurround ring 1441 can be made of, for instance, silicon carbide orgraphite.

In FIG. 14G, susceptor cloth 1457, which is made of, for instance,silicon carbide or graphite, is dropped into pocket 1403. Wafer surroundring 1451, which is made of quartz, is placed on top of susceptor cloth1457. Wafer 1404 is placed into a recess formed in wafer surround ring1451.

In the above embodiments of FIGS. 14A-14G, the particular dimensions ofthe wafer surround ring, susceptor cloth, spindle and susceptor insertare determined empirically to minimize slip and maintain substantiallyuniform temperature in wafer 1404. Additionally, where quartz can beused in lieu of silicon carbide or graphite, the choice is made as aresult of weighing the desirable heat retention of graphite or siliconcarbide against the undesirable thermal inertia of those materials.Further, where quartz is used for a susceptor insert, spindle or wafersurround ring, the surface of the quartz can be bead-blasted or clear.Bead-blasting causes the quartz to retain more heat.

In reactor 400, there is an area of substantially uniform temperature atthe center of reaction chamber 403 outside of which the wafer or-wafersbeing processed must not extend if substantially uniform temperature isto be maintained throughout the wafer or wafers during processing.However, within that region of substantially uniform temperature, awafer or wafers may be mounted at any location on susceptor 402. FIGS.15A, 15B and 15C are top views of three susceptors 1502, 1522, 1542 foruse with reactor 400 illustrating three possible ways of mounting awafer or wafers.

In FIG. 15A, wafer 1511 is mounted so that center 1511a of wafer 1511 is2 inches (5.08 cm) from center 1502a of susceptor 1502. The large regionof temperature uniformity established in reactor 400 maintainssubstantially uniform temperature throughout wafer 1511 even thoughwafer 1511 is not centered on susceptor 402 (i.e., wafer 1511 is notcentered within reaction chamber 403). This off-center mounting isdesirable because, with susceptor 1502 rotated into proper position, thedistance that the wafer loading arm must travel in order to load wafer1511 is minimized, thus reducing the chance that problems (e.g.,misalignment of wafer 1511 on susceptor 1502) occur in the waferhandling process.

In FIG. 15B, wafer 1531 is mounted such that center 1531a of wafer 1531is coincident with center 1522a of susceptor 1522 and, therefore, isapproximately centered within the region of substantially uniformtemperature in reaction chamber 403. Because of this centering, wafers1531 processed with susceptor 1522 can be larger than wafers 1511processed with susceptor 1502.

In FIG. 15C, wafers 1551, 1552, 1553 are located symmetrically onsusceptor 1542. Centers 1551a, 1552a, 1553a of wafers 1551, 1552, 1553,respectively, are located 3.783 inches (9.609 cm) from center 1542a ofsusceptor 1542. Centers 1551a, 1552a, 1553a of wafers 1551, 1552, 1553,respectively, are located at an angle α of 120° with respect to eachother in a radial direction around susceptor 1542. Since-more than onewafer is being processed at a time, in order to maintain wafers 1551,1552, 1553 within the region of substantially uniform temperature inreaction chamber 403, the maximum size of wafers 1551, 1552, 1553 issmaller than the maximum size of wafer 1531 in FIG. 15B.

Though FIGS. 15A, 15B and 15C show either one or three wafers on asusceptor, susceptors on which two, four or more wafers are mounted canalso be used with reactors according to the invention. However, thenumber of wafers that may be processed at one time is limited by thesize of the wafers being processed.

FIGS. 15D and 15E are plan views of susceptors 1562 and 1582,respectively, for use with reactor 400, on which three 150 mm (6 inch)wafers 1571a, 1571b, 1571c and one 200 mm (8 inch) wafer 1591,respectively, are mounted. In FIG. 15D, holes 1563a , 1563b, 1563c,1563d, 1563e, 1563f, 1563g, 1563h, 1563i, formed through susceptor 1562to allow wafer support pins 513 to extend to raise wafer 1571a, 1571b,1571c above susceptor 1562. Each wafer 1571a, 1571b, 1571c is raised byrotating susceptor 1562 so that wafer 1571a, 1571b or 1571c is inposition above mounting rods 512b, 512c, 512d. In FIG. 15E, holes 1583a,1583b, 1583c, 1583d, 1583e are formed through susceptor 1582 to allowwafer support pins 513 to extend so that they can raise wafer 1591 abovesusceptor 1582. Wafer 1591 is raised by rotating susceptor 1582 so thatwafer 1591 is in position above mounting rods 512a, 512b, 512c, 512d,512e. Mounting rods 512a, 512b, 512c, 512d or mounting rods 512b, 512c,512e can be used to raise wafer 1591.

As previously described, reactant gases from a gas panel are inlet intoreaction chamber 403 through gas inlet tube 408a through either a gasinjection head, e.g., gas injection head 414, or gas injection jets 421,and exhausted through exhaust lines 409a, 409b, 409c out of reactor 400to a scrubber that cleans the gases before exhausting them to theatmosphere. In previous reactors, separate computers have been used tocontrol the gas distribution system and scrubber individually.

FIG. 16 is a simplified view of a reactor 1600 according to theinvention in which a single computer 1610 is used to control both gaspanel 1601 and scrubber 1606. Reactant gases are distributed from gaspanel 1601 through gas inlet 1602 to reaction chamber 1603. The gasesflow through reaction chamber 1603 past wafer 1604 and are exhaustedthrough gas exhaust 1605 to scrubber 1606. Scrubber 1606 cleans thegases and discharges them through scrubber exhaust 1607 to theatmosphere.

Computer 1610 controls the type and flow rate of gases distributed fromgas panel 1601 via gas distribution control line 1608 according tooperator specified data stored in computer 1610 for the desired process.Likewise, computer 1610 controls the cleansing operation of scrubber1606 via scrubber control line 1609 according to other operatorspecified data stored in computer 1610 that are appropriate for theprocess gases used. Thus, in reactor 1600, unlike previous reactors,computer control of gas distribution and scrubbing, which areinterrelated operations, is made easier since the data for eachoperation is stored and manipulated by one device.

In one embodiment of this invention, the process computer, as describedabove, controls the interlocks used in operation of the reactor as wellas the temperature process controls, power control, etc. While thereactor of this invention includes many novel features, the operation ofthe process computer is similar to other reactors when the novelfeatures described herein are taken into consideration. Nevertheless, anexample of software used in the process computer for initial operationaltesting is presented in Microfiche Appendix A, which is incorporatedherein by reference in its entirety. A computer suitable for thisinvention is manufactured by Prolog and is available from WesternTechnology Marketing of Mountain View, Calif. as Model No. CR345-01.

In another embodiment, in addition to process control of the reactor,the process computer includes a database of statistical data for eachprocess run as well as the reactor configuration for each process run.When the database contains sufficient data for significant statisticalanalysis, the process computer takes complete control of the processcycle. The reactor operator simply enters information concerning thebatch size, the desired process, and the required uniformities. Theprocess computer takes this information and analyzes the database todetermine the correct process parameters for the run. The processcomputer then automatically configures the reactor and automaticallyruns the process to obtain the results specified by the reactoroperator.

Further, unlike prior art systems that had a computer for the reactor,another computer to control the gas cabinets, and yet another computerto control the scrubbers, the process computer of this invention willhandle all of these operations. Thus, from a single console, the reactoroperator can configure the gas panel to deliver gases in a particularsequence for a particular process and can configure the scrubber toprocess the exhaust gases as required. Centralization of theseoperations into a single computer reduces the hardware costs and moreimportantly reduces the time required to configure the entire systemthereby further enhancing the batch cycle time.

Since, as noted above, a reactor according to the invention can be usedfor any of a number of semiconductor processes, it is possible toassemble a group of reactors to perform a sequential set of steps in asemiconductor process flow. FIG. 17 is a top view of a cluster ofreactors 1710, 1720, 1730, 1740 according to the invention, each ofwhich is used to perform a particular semiconductor process (e.g.,deposition, annealing, etc.). Reactors 1710, 1720, 1730 and 1740 arearranged around sealed chamber 1705 in which robot 1704 is located. Aplurality of wafer cassettes 1702a, 1702b, 1702c, each containing aplurality of wafers stacked on top of each other, are located incassette room 1703 adjacent clean room 1701. Wafer cassettes 1702a,1702b, 1702c are first transferred from clean room 1701 to cassette room1703. A computer control system is used to direct robot 1704 to take anappropriate wafer from a wafer cassette, e.g., wafer cassette 1702a,from cassette room 1703 and load it into an appropriate reactionchamber, e.g., reaction chamber 1740a, of a reactor, e.g., reactor 1740.Robot 1704 is also controlled to transfer wafers from one reactionchamber, e.g., reaction chamber 1740a, to another reaction chamber,e.g., reaction chamber 1720a. Consequently, a semiconductor process flowcan be automated and quickly performed using robot 1704 and a group ofreactors, e.g., reactors 1710, 1720, 1730, 1740 according to theinvention. Though four reactors 1710, 1720, 1730, 1740 are shown in FIG.17, it is to be understood that two, three, five or more reactorsaccording to the invention could be arranged in a similar manner.

As noted above with respect to reactor 400 of FIG. 4A and 4B, it isdesirable to be able to pivot shell 452 of reactor 400 away from vessel401 when maintenance is to be performed on reactor 400. Spacelimitations may make it preferable to pivot shell 452 to one side or theother of reactor 400. According to the invention, shell 452 may beeasily pivoted to either side of reactor 400. In FIG. 17, reactor 1720is shown with shell 1720b pivoted to a first side of reactor 1720, andreactor 1740 is shown with shell 1740b pivoted to a second side ofreactor 1740.

Above, various embodiments of the invention have been described. Thedescriptions are intended to be illustrative, not limitative. Thus, itwill be apparent to one skilled in the art that certain modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

We claim:
 1. In a reactor for processing a substrate, a structurecomprising:a susceptor having a first surface adapted for mounting asubstrate thereon; a second surface; and a plurality of openingsextending through said susceptor from said first surface to said secondsurface wherein each opening in said plurality of openings extendingthrough said susceptor from said first surface to said second surfacehas a surface; and a plurality of substrate support pins;wherein asubstrate support pin is movably mounted in each of said plurality ofopenings and in a first position said substrate support pins are seatedin said susceptor when said substrate is supported by said susceptor,and in a second position said substrate support pins hold said substrateabove said first surface; and each substrate support pin in saidplurality of substrate support pins has a surface wherein in said firstposition, the surface on the substrate support pin mates with thesurface of the opening so as to inhibit gas flow through said pluralityof openings in said susceptor during processing.
 2. In a reactor forprocessing a substrate, the structure of claim 1 further comprising;aplurality of supports, one for each substrate support pin, mounted insaid reactor so that when said susceptor is in a third position, saidplurality of supports hold said plurality of substrate support pins insaid second position.
 3. In a reactor for processing a substrate, thestructure of claim 2 wherein when said susceptor is in a fourthposition, said plurality of substrate support pins are in said firstposition.
 4. In a reactor for processing a substrate, a structure as inclaim 1 wherein said surface of said opening and said surface of saidsubstrate support pin are both tapered so that said tapered surface ofsaid substrate support pin mates with tapered surface of said opening issaid first position.
 5. A rapid thermal process reactor comprising:areaction chamber; a rotatable susceptor mounted within the reactionchamber, and having:a first surface adapted for supporting at least onesubstrate; a second surface; a plurality of openings extending throughsaid rotatable susceptor from said first surface to said second surfacewith each opening in said plurality of openings extending through saidrotatable susceptor from said first surface to said second surfacehaving a surface; and a plurality of substrate support pinswherein asubstrate support pin is movably mounted in each of said plurality ofopenings and in a first position said substrate support pins are seatedin said susceptor when said at least one substrate is supported by saidsusceptor, and in a second position said substrate support pins holdsaid at least one substrate above said first surface; and each substratesupport pin in said plurality of substrate support pins has a surfacewherein in said first position, the surface on the substrate support pinmates with the surface of the opening so as to inhibit gas flow throughsaid plurality of openings in said susceptor during processing; and aradiant heat source mounted outside said reaction chamber so thatradiant heat from said heat source directly heats said at least onesubstrate.
 6. A rapid thermal process reactor as in claim 5 furthercomprising:a plurality of gas jets mounted within said rapid thermalprocess reaction chamber about an outer circumference of said rotatablerapid thermal process susceptor.